Commit Graph

155 Commits

Author SHA1 Message Date
Mauro Carvalho Chehab
99c8b231ae docs: cgroup-v1: convert docs to ReST and rename to *.rst
Convert the cgroup-v1 files to ReST format, in order to
allow a later addition to the admin-guide.

The conversion is actually:
  - add blank lines and identation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
2019-06-14 13:29:54 -07:00
Minwoo Im
0d413829bd block: null: Add documentation for "zone_nr_conv" param
zone_nr_conv module parameter was introduced by a commit
ea2c18e1("null_blk: Add conventional zone configuration for zoned
support").

This patch describes "zone_nr_conv" module parameter to the document.

Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-04-09 08:18:23 -06:00
Paolo Valente
4438cf50e7 doc, block, bfq: add information on bfq execution time
The execution time of BFQ has been slightly lowered. Report the new
execution time in BFQ documentation.

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-04-01 08:15:40 -06:00
Ming Lei
ac4fa1d107 block: document usage of bio iterator helpers
Now multi-page bvec is supported, some helpers may return page by
page, meantime some may return segment by segment, this patch
documents the usage.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-15 08:40:12 -07:00
John Pittman
47cb393ee4 block: doc: add slice_idle_us to bfq documentation
Of the tunables available for the bfq I/O scheduler, the only one
missing from the documentation in 'Documentation/block/bfq-iosched.txt'
is slice_idle_us. Add this tunable to the documentation and a short
explanation of its purpose.

Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: John Pittman <jpittman@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-01-09 07:38:48 -07:00
John Pittman
373282e7ab null_blk: add zoned config support information
If the kernel is built without CONFIG_BLK_DEV_ZONED, a modprobe
of the null_blk driver with zoned=1 fails with 'Invalid argument'.
This can be confusing to users, prompting a search as to why the
parameter is invalid. To assist in that search, add a bit more
information to the failure, additionally adding to the documentation
that CONFIG_BLK_DEV_ZONED is needed for zoned=1.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: John Pittman <jpittman@redhat.com>

Added null_blk prefix to error message.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-01-06 10:58:27 -07:00
Weiping Zhang
bb351abaf5 block: add documentation for io_timeout
Add documentation for /sys/block/<disk>/queue/io_timeout.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Weiping Zhang <zhangweiping@didiglobal.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-01-04 19:19:51 -07:00
Damien Le Moal
f9824952ee block: update sysfs documentation
Add the description of the zoned, nr_zones and chunk_sectors sysfs queue
attributes to Documentation/block/queue-sysfs.txt. The description of
the zoned and chunk_sector attributes are mostly copied from
ABI/testing/sysfs-block (added a typo fix). While at it, also fix a
typo in the description of the io_poll_delay attribute.

nr_zones description is also added to ABI/testing/sysfs-block and
contact email address updated for the zoned attribute.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-12-16 19:53:06 -07:00
Jens Axboe
f382fb0bce block: remove legacy IO schedulers
Retain the deadline documentation, as that carries over to mq-deadline
as well.

Tested-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-11-07 13:42:32 -07:00
Jens Axboe
7ca0192646 block: remove legacy rq tagging
It's now unused, kill it.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-11-07 13:42:32 -07:00
Henrik Austad
a7ddcea58a Drop all 00-INDEX files from Documentation/
This is a respin with a wider audience (all that get_maintainer returned)
and I know this spams a *lot* of people. Not sure what would be the correct
way, so my apologies for ruining your inbox.

The 00-INDEX files are supposed to give a summary of all files present
in a directory, but these files are horribly out of date and their
usefulness is brought into question. Often a simple "ls" would reveal
the same information as the filenames are generally quite descriptive as
a short introduction to what the file covers (it should not surprise
anyone what Documentation/sched/sched-design-CFS.txt covers)

A few years back it was mentioned that these files were no longer really
needed, and they have since then grown further out of date, so perhaps
it is time to just throw them out.

A short status yields the following _outdated_ 00-INDEX files, first
counter is files listed in 00-INDEX but missing in the directory, last
is files present but not listed in 00-INDEX.

List of outdated 00-INDEX:
Documentation: (4/10)
Documentation/sysctl: (0/1)
Documentation/timers: (1/0)
Documentation/blockdev: (3/1)
Documentation/w1/slaves: (0/1)
Documentation/locking: (0/1)
Documentation/devicetree: (0/5)
Documentation/power: (1/1)
Documentation/powerpc: (0/5)
Documentation/arm: (1/0)
Documentation/x86: (0/9)
Documentation/x86/x86_64: (1/1)
Documentation/scsi: (4/4)
Documentation/filesystems: (2/9)
Documentation/filesystems/nfs: (0/2)
Documentation/cgroup-v1: (0/2)
Documentation/kbuild: (0/4)
Documentation/spi: (1/0)
Documentation/virtual/kvm: (1/0)
Documentation/scheduler: (0/2)
Documentation/fb: (0/1)
Documentation/block: (0/1)
Documentation/networking: (6/37)
Documentation/vm: (1/3)

Then there are 364 subdirectories in Documentation/ with several files that
are missing 00-INDEX alltogether (and another 120 with a single file and no
00-INDEX).

I don't really have an opinion to whether or not we /should/ have 00-INDEX,
but the above 00-INDEX should either be removed or be kept up to date. If
we should keep the files, I can try to keep them updated, but I rather not
if we just want to delete them anyway.

As a starting point, remove all index-files and references to 00-INDEX and
see where the discussion is going.

Signed-off-by: Henrik Austad <henrik@austad.us>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Just-do-it-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Paul Moore <paul@paul-moore.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: [Almost everybody else]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2018-09-09 15:08:58 -06:00
Michael Callahan
bdca3c87fb block: Track DISCARD statistics and output them in stat and diskstat
Add tracking of REQ_OP_DISCARD ios to the partition statistics and
append them to the various stat files in /sys as well as
/proc/diskstats.  These are tracked with the same four stats as reads
and writes:

Number of discard ios completed.
Number of discard ios merged
Number of discard sectors completed
Milliseconds spent on discard requests

This is done via adding a new STAT_DISCARD define to genhd.h and then
using it to index that stat field for discard requests.

tj: Refreshed on top of v4.17 and other previous updates.

Signed-off-by: Michael Callahan <michaelcallahan@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-07-18 08:44:22 -06:00
Matias Bjørling
ca4b2a0119 null_blk: add zone support
Adds support for exposing a null_blk device through the zone device
interface.

The interface is managed with the parameters zoned and zone_size.
If zoned is set, the null_blk instance registers as a zoned block
device. The zone_size parameter defines how big each zone will be.

Signed-off-by: Matias Bjørling <matias.bjorling@wdc.com>
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-07-09 09:07:55 -06:00
Christoph Hellwig
be7f99c536 block: remov blk_queue_invalidate_tags
This function is entirely unused, so remove it and the tag_queue_busy
member of struct request_queue.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-06-15 08:13:35 -06:00
Linus Torvalds
eeee3149aa There's been a fair amount of work in the docs tree this time around,
including:
 
  - Extensive RST conversions and organizational work in the
    memory-management docs thanks to Mike Rapoport.
 
  - An update of Documentation/features from Andrea Parri and a script to
    keep it updated.
 
  - Various LICENSES updates from Thomas, along with a script to check SPDX
    tags.
 
  - Work to fix dangling references to documentation files; this involved a
    fair number of one-liner comment changes outside of Documentation/
 
 ...and the usual list of documentation improvements, typo fixes, etc.
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Merge tag 'docs-4.18' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "There's been a fair amount of work in the docs tree this time around,
  including:

   - Extensive RST conversions and organizational work in the
     memory-management docs thanks to Mike Rapoport.

   - An update of Documentation/features from Andrea Parri and a script
     to keep it updated.

   - Various LICENSES updates from Thomas, along with a script to check
     SPDX tags.

   - Work to fix dangling references to documentation files; this
     involved a fair number of one-liner comment changes outside of
     Documentation/

  ... and the usual list of documentation improvements, typo fixes, etc"

* tag 'docs-4.18' of git://git.lwn.net/linux: (103 commits)
  Documentation: document hung_task_panic kernel parameter
  docs/admin-guide/mm: add high level concepts overview
  docs/vm: move ksm and transhuge from "user" to "internals" section.
  docs: Use the kerneldoc comments for memalloc_no*()
  doc: document scope NOFS, NOIO APIs
  docs: update kernel versions and dates in tables
  docs/vm: transhuge: split userspace bits to admin-guide/mm/transhuge
  docs/vm: transhuge: minor updates
  docs/vm: transhuge: change sections order
  Documentation: arm: clean up Marvell Berlin family info
  Documentation: gpio: driver: Fix a typo and some odd grammar
  docs: ranoops.rst: fix location of ramoops.txt
  scripts/documentation-file-ref-check: rewrite it in perl with auto-fix mode
  docs: uio-howto.rst: use a code block to solve a warning
  mm, THP, doc: Add document for thp_swpout/thp_swpout_fallback
  w1: w1_io.c: fix a kernel-doc warning
  Documentation/process/posting: wrap text at 80 cols
  docs: admin-guide: add cgroup-v2 documentation
  Revert "Documentation/features/vm: Remove arch support status file for 'pte_special'"
  Documentation: refcount-vs-atomic: Update reference to LKMM doc.
  ...
2018-06-04 12:34:27 -07:00
Liu Bo
6723d8dc9d null_blk: add blocking description and remove lightnvm
- The description of 'blocking' is missing in null_blk.txt

- The 'lightnvm' parameter has been removed in null_blk.c

This updates both in null_blk.txt.

Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-05-25 08:51:58 -06:00
Randy Dunlap
f6dbf65b65 Documentation: block: cmdline-partition.txt fixes and additions
Make the description of the kernel command line option "blkdevparts"
a bit more flowing and readable.

Fix a few typos.
Add the optional <size> and <offset> suffixes.
Note that size can be "-" to indicate all of the remaining space.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Cai Zhiyong <caizhiyong@huawei.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2018-05-08 09:18:53 -06:00
Luca Miccio
a33801e8b4 block, bfq: move debug blkio stats behind CONFIG_DEBUG_BLK_CGROUP
BFQ currently creates, and updates, its own instance of the whole
set of blkio statistics that cfq creates. Yet, from the comments
of Tejun Heo in [1], it turned out that most of these statistics
are meant/useful only for debugging. This commit makes BFQ create
the latter, debugging statistics only if the option
CONFIG_DEBUG_BLK_CGROUP is set.

By doing so, this commit also enables BFQ to enjoy a high perfomance
boost. The reason is that, if CONFIG_DEBUG_BLK_CGROUP is not set, then
BFQ has to update far fewer statistics, and, in particular, not the
heaviest to update.  To give an idea of the benefits, if
CONFIG_DEBUG_BLK_CGROUP is not set, then, on an Intel i7-4850HQ, and
with 8 threads doing random I/O in parallel on null_blk (configured
with 0 latency), the throughput of BFQ grows from 310 to 400 KIOPS
(+30%). We have measured similar or even much higher boosts with other
CPUs: e.g., +45% with an ARM CortexTM-A53 Octa-core. Our results have
been obtained and can be reproduced very easily with the script in [1].

[1] https://www.spinics.net/lists/linux-block/msg18943.html

Suggested-by: Tejun Heo <tj@kernel.org>
Suggested-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Lee Tibbert <lee.tibbert@gmail.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Luca Miccio <lucmiccio@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-11-14 20:13:33 -07:00
Paolo Valente
24bfd19bb7 block, bfq: update blkio stats outside the scheduler lock
bfq invokes various blkg_*stats_* functions to update the statistics
contained in the special files blkio.bfq.* in the blkio controller
groups, i.e., the I/O accounting related to the proportional-share
policy provided by bfq. The execution of these functions takes a
considerable percentage, about 40%, of the total per-request execution
time of bfq (i.e., of the sum of the execution time of all the bfq
functions that have to be executed to process an I/O request from its
creation to its destruction).  This reduces the request-processing
rate sustainable by bfq noticeably, even on a multicore CPU. In fact,
the bfq functions that invoke blkg_*stats_* functions cannot be
executed in parallel with the rest of the code of bfq, because both
are executed under the same same per-device scheduler lock.

To reduce this slowdown, this commit moves, wherever possible, the
invocation of these functions (more precisely, of the bfq functions
that invoke blkg_*stats_* functions) outside the critical sections
protected by the scheduler lock.

With this change, and with all blkio.bfq.* statistics enabled, the
throughput grows, e.g., from 250 to 310 KIOPS (+25%) on an Intel
i7-4850HQ, in case of 8 threads doing random I/O in parallel on
null_blk, with the latter configured with 0 latency. We obtained the
same or higher throughput boosts, up to +30%, with other processors
(some figures are reported in the documentation). For our tests, we
used the script [1], with which our results can be easily reproduced.

NOTE. This commit still protects the invocation of blkg_*stats_*
functions with the request_queue lock, because the group these
functions are invoked on may otherwise disappear before or while these
functions are executed.  Fortunately, tests without even this lock
show, by difference, that the serialization caused by this lock has a
little impact (at most ~5% of throughput reduction).

[1] https://github.com/Algodev-github/IOSpeed

Tested-by: Lee Tibbert <lee.tibbert@gmail.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Luca Miccio <lucmiccio@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-11-14 20:13:33 -07:00
Paolo Valente
68017e5d87 doc, block, bfq: update max IOPS sustainable with BFQ
We have investigated more deeply the performance of BFQ, in terms of
number of IOPS that can be processed by the CPU when BFQ is used as
I/O scheduler. In more detail, using the script [1], we have measured
the number of IOPS reached on top of a null block device configured
with zero latency, as a function of the workload (sequential read,
sequential write, random read, random write) and of the system (we
considered desktops, laptops and embedded systems).

Basing on the resulting figures, with this commit we update the
current, conservative IOPS range reported in BFQ documentation. In
particular, the documentation now reports, for each of three different
systems, the lowest number of IOPS obtained for that system with the
above test (namely, the value obtained with the workload leading to
the lowest IOPS).

[1] https://github.com/Algodev-github/IOSpeed

Reviewed-by: Lee Tibbert <lee.tibbert@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Luca Miccio <lucmiccio@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-11-14 20:13:33 -07:00
Christoph Hellwig
d004a5e7d4 block: remove __bio_kmap_atomic
This helper doesn't buy us much over calling kmap_atomic directly.
In fact in the only caller it does a bit of useless work as the
caller already has the bvec at hand, and said caller would even
buggy for a multi-segment bio due to the use of this helper.

So just remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-11-10 19:53:25 -07:00
Jens Axboe
83f5f7ed72 block: kill bio_kmap/kunmap_irq()
There are no users of it anymore.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-11-10 19:53:25 -07:00
Minwoo Im
bf9fc98b73 null_blk: add an usage for shared tags in documentation
Add usage explanation for a shared_tags, introduced by commit:

82f402fefa ("null_blk: add support for shared tags")

Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>

Reworded slightly.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-11-07 09:25:37 -07:00
Minwoo Im
e881524117 null_blk: fix default values in documentation
null_blk.c has initial value of
(1) nr_devices as 1.
(2) completion_nsec as 10,000ns, not 10.000ns.
documentation should be updated for fixes above.

Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-11-07 09:24:06 -07:00
weiping zhang
fc186311f2 null_blk: add usage hints for no_sched
This parameter provide an option to disable io scheduler when nullb*
in multi-queue mode.

Signed-off-by: weiping zhang <zhangweiping@didichuxing.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-10-13 10:52:39 -06:00
weiping zhang
23c4490d2b null_blk: update usage hints for submit_queues
update the range of submits_queues, and correct usage hints.

Signed-off-by: weiping zhang <zhangweiping@didichuxing.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-10-13 10:52:37 -06:00
Paolo Valente
2670cd1674 doc, block, bfq: better describe how to properly configure bfq
Many users have reported the lack of an HOWTO for properly configuring
bfq as a function of the goal one wants to achieve (max
responsiveness, max throughput, ...). In fact, all needed details are
already provided in the documentation file bfq-iosched.txt. Yet the
document lacks guidance on which parameter descriptions to look
at. This commit adds some simple direction.

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Reviewed-by: Jeremy Hickman <jeremywh7@gmail.com>
Reviewed-by: Laurentiu Nicola <lnicola@dend.ro>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-08-31 13:55:26 -06:00
Paolo Valente
233f0bf415 doc, block, bfq: fix some typos and remove stale stuff
In addition to containing some typos and stale sentences, the file
bfq-iosched.txt still mentioned a set of sysfs parameters that have
been removed from this version of bfq. This commit fixes all these
issues.

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Reviewed-by: Jeremy Hickman <jeremywh7@gmail.com>
Reviewed-by: Laurentiu Nicola <lnicola@dend.ro>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-08-31 13:55:25 -06:00
Dmitry Monakhov
e23947bd76 bio-integrity: fold bio_integrity_enabled to bio_integrity_prep
Currently all integrity prep hooks are open-coded, and if prepare fails
we ignore it's code and fail bio with EIO. Let's return real error to
upper layer, so later caller may react accordingly.

In fact no one want to use bio_integrity_prep() w/o bio_integrity_enabled,
so it is reasonable to fold it in to one function.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
[hch: merged with the latest block tree,
	return bool from bio_integrity_prep]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-07-03 16:56:24 -06:00
NeilBrown
9b10f6a9c2 block: remove bio_clone() and all references.
bio_clone() is no longer used.
Only bio_clone_bioset() or bio_clone_fast().
This is for the best, as bio_clone() used fs_bio_set,
and filesystems are unlikely to want to use bio_clone().

So remove bio_clone() and all references.
This includes a fix to some incorrect documentation.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-06-18 12:40:59 -06:00
Paolo Valente
43c1b3d6e5 block, bfq: stress that low_latency must be off to get max throughput
The introduction of the BFQ and Kyber I/O schedulers has triggered a
new wave of I/O benchmarks. Unfortunately, comments and discussions on
these benchmarks confirm that there is still little awareness that it
is very hard to achieve, at the same time, a low latency and a high
throughput. In particular, virtually all benchmarks measure
throughput, or throughput-related figures of merit, but, for BFQ, they
use the scheduler in its default configuration. This configuration is
geared, instead, toward a low latency. This is evidently a sign that
BFQ documentation is still too unclear on this important aspect. This
commit addresses this issue by stressing how BFQ configuration must be
(easily) changed if the only goal is maximum throughput.

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-05-10 07:39:43 -06:00
Paolo Valente
44e44a1b32 block, bfq: improve responsiveness
This patch introduces a simple heuristic to load applications quickly,
and to perform the I/O requested by interactive applications just as
quickly. To this purpose, both a newly-created queue and a queue
associated with an interactive application (we explain in a moment how
BFQ decides whether the associated application is interactive),
receive the following two special treatments:

1) The weight of the queue is raised.

2) The queue unconditionally enjoys device idling when it empties; in
fact, if the requests of a queue are sync, then performing device
idling for the queue is a necessary condition to guarantee that the
queue receives a fraction of the throughput proportional to its weight
(see [1] for details).

For brevity, we call just weight-raising the combination of these
two preferential treatments. For a newly-created queue,
weight-raising starts immediately and lasts for a time interval that:
1) depends on the device speed and type (rotational or
non-rotational), and 2) is equal to the time needed to load (start up)
a large-size application on that device, with cold caches and with no
additional workload.

Finally, as for guaranteeing a fast execution to interactive,
I/O-related tasks (such as opening a file), consider that any
interactive application blocks and waits for user input both after
starting up and after executing some task. After a while, the user may
trigger new operations, after which the application stops again, and
so on. Accordingly, the low-latency heuristic weight-raises again a
queue in case it becomes backlogged after being idle for a
sufficiently long (configurable) time. The weight-raising then lasts
for the same time as for a just-created queue.

According to our experiments, the combination of this low-latency
heuristic and of the improvements described in the previous patch
allows BFQ to guarantee a high application responsiveness.

[1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
    Scheduler", Proceedings of the First Workshop on Mobile System
    Technologies (MST-2015), May 2015.
    http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-04-19 08:30:26 -06:00
Arianna Avanzini
e21b7a0b98 block, bfq: add full hierarchical scheduling and cgroups support
Add complete support for full hierarchical scheduling, with a cgroups
interface. Full hierarchical scheduling is implemented through the
'entity' abstraction: both bfq_queues, i.e., the internal BFQ queues
associated with processes, and groups are represented in general by
entities. Given the bfq_queues associated with the processes belonging
to a given group, the entities representing these queues are sons of
the entity representing the group. At higher levels, if a group, say
G, contains other groups, then the entity representing G is the parent
entity of the entities representing the groups in G.

Hierarchical scheduling is performed as follows: if the timestamps of
a leaf entity (i.e., of a bfq_queue) change, and such a change lets
the entity become the next-to-serve entity for its parent entity, then
the timestamps of the parent entity are recomputed as a function of
the budget of its new next-to-serve leaf entity. If the parent entity
belongs, in its turn, to a group, and its new timestamps let it become
the next-to-serve for its parent entity, then the timestamps of the
latter parent entity are recomputed as well, and so on. When a new
bfq_queue must be set in service, the reverse path is followed: the
next-to-serve highest-level entity is chosen, then its next-to-serve
child entity, and so on, until the next-to-serve leaf entity is
reached, and the bfq_queue that this entity represents is set in
service.

Writeback is accounted for on a per-group basis, i.e., for each group,
the async I/O requests of the processes of the group are enqueued in a
distinct bfq_queue, and the entity associated with this queue is a
child of the entity associated with the group.

Weights can be assigned explicitly to groups and processes through the
cgroups interface, differently from what happens, for single
processes, if the cgroups interface is not used (as explained in the
description of the previous patch). In particular, since each node has
a full scheduler, each group can be assigned its own weight.

Signed-off-by: Fabio Checconi <fchecconi@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-04-19 08:30:26 -06:00
Paolo Valente
aee69d78de block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler
We tag as v0 the version of BFQ containing only BFQ's engine plus
hierarchical support. BFQ's engine is introduced by this commit, while
hierarchical support is added by next commit. We use the v0 tag to
distinguish this minimal version of BFQ from the versions containing
also the features and the improvements added by next commits. BFQ-v0
coincides with the version of BFQ submitted a few years ago [1], apart
from the introduction of preemption, described below.

BFQ is a proportional-share I/O scheduler, whose general structure,
plus a lot of code, are borrowed from CFQ.

- Each process doing I/O on a device is associated with a weight and a
  (bfq_)queue.

- BFQ grants exclusive access to the device, for a while, to one queue
  (process) at a time, and implements this service model by
  associating every queue with a budget, measured in number of
  sectors.

  - After a queue is granted access to the device, the budget of the
    queue is decremented, on each request dispatch, by the size of the
    request.

  - The in-service queue is expired, i.e., its service is suspended,
    only if one of the following events occurs: 1) the queue finishes
    its budget, 2) the queue empties, 3) a "budget timeout" fires.

    - The budget timeout prevents processes doing random I/O from
      holding the device for too long and dramatically reducing
      throughput.

    - Actually, as in CFQ, a queue associated with a process issuing
      sync requests may not be expired immediately when it empties. In
      contrast, BFQ may idle the device for a short time interval,
      giving the process the chance to go on being served if it issues
      a new request in time. Device idling typically boosts the
      throughput on rotational devices, if processes do synchronous
      and sequential I/O. In addition, under BFQ, device idling is
      also instrumental in guaranteeing the desired throughput
      fraction to processes issuing sync requests (see [2] for
      details).

      - With respect to idling for service guarantees, if several
        processes are competing for the device at the same time, but
        all processes (and groups, after the following commit) have
        the same weight, then BFQ guarantees the expected throughput
        distribution without ever idling the device. Throughput is
        thus as high as possible in this common scenario.

  - Queues are scheduled according to a variant of WF2Q+, named
    B-WF2Q+, and implemented using an augmented rb-tree to preserve an
    O(log N) overall complexity.  See [2] for more details. B-WF2Q+ is
    also ready for hierarchical scheduling. However, for a cleaner
    logical breakdown, the code that enables and completes
    hierarchical support is provided in the next commit, which focuses
    exactly on this feature.

  - B-WF2Q+ guarantees a tight deviation with respect to an ideal,
    perfectly fair, and smooth service. In particular, B-WF2Q+
    guarantees that each queue receives a fraction of the device
    throughput proportional to its weight, even if the throughput
    fluctuates, and regardless of: the device parameters, the current
    workload and the budgets assigned to the queue.

  - The last, budget-independence, property (although probably
    counterintuitive in the first place) is definitely beneficial, for
    the following reasons:

    - First, with any proportional-share scheduler, the maximum
      deviation with respect to an ideal service is proportional to
      the maximum budget (slice) assigned to queues. As a consequence,
      BFQ can keep this deviation tight not only because of the
      accurate service of B-WF2Q+, but also because BFQ *does not*
      need to assign a larger budget to a queue to let the queue
      receive a higher fraction of the device throughput.

    - Second, BFQ is free to choose, for every process (queue), the
      budget that best fits the needs of the process, or best
      leverages the I/O pattern of the process. In particular, BFQ
      updates queue budgets with a simple feedback-loop algorithm that
      allows a high throughput to be achieved, while still providing
      tight latency guarantees to time-sensitive applications. When
      the in-service queue expires, this algorithm computes the next
      budget of the queue so as to:

      - Let large budgets be eventually assigned to the queues
        associated with I/O-bound applications performing sequential
        I/O: in fact, the longer these applications are served once
        got access to the device, the higher the throughput is.

      - Let small budgets be eventually assigned to the queues
        associated with time-sensitive applications (which typically
        perform sporadic and short I/O), because, the smaller the
        budget assigned to a queue waiting for service is, the sooner
        B-WF2Q+ will serve that queue (Subsec 3.3 in [2]).

- Weights can be assigned to processes only indirectly, through I/O
  priorities, and according to the relation:
  weight = 10 * (IOPRIO_BE_NR - ioprio).
  The next patch provides, instead, a cgroups interface through which
  weights can be assigned explicitly.

- If several processes are competing for the device at the same time,
  but all processes and groups have the same weight, then BFQ
  guarantees the expected throughput distribution without ever idling
  the device. It uses preemption instead. Throughput is then much
  higher in this common scenario.

- ioprio classes are served in strict priority order, i.e.,
  lower-priority queues are not served as long as there are
  higher-priority queues.  Among queues in the same class, the
  bandwidth is distributed in proportion to the weight of each
  queue. A very thin extra bandwidth is however guaranteed to the Idle
  class, to prevent it from starving.

- If the strict_guarantees parameter is set (default: unset), then BFQ
     - always performs idling when the in-service queue becomes empty;
     - forces the device to serve one I/O request at a time, by
       dispatching a new request only if there is no outstanding
       request.
  In the presence of differentiated weights or I/O-request sizes,
  both the above conditions are needed to guarantee that every
  queue receives its allotted share of the bandwidth (see
  Documentation/block/bfq-iosched.txt for more details). Setting
  strict_guarantees may evidently affect throughput.

[1] https://lkml.org/lkml/2008/4/1/234
    https://lkml.org/lkml/2008/11/11/148

[2] P. Valente and M. Andreolini, "Improving Application
    Responsiveness with the BFQ Disk I/O Scheduler", Proceedings of
    the 5th Annual International Systems and Storage Conference
    (SYSTOR '12), June 2012.
    Slightly extended version:
    http://algogroup.unimore.it/people/paolo/disk_sched/bfq-v1-suite-
							results.pdf

Signed-off-by: Fabio Checconi <fchecconi@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-04-19 08:29:02 -06:00
Omar Sandoval
00e043936e blk-mq: introduce Kyber multiqueue I/O scheduler
The Kyber I/O scheduler is an I/O scheduler for fast devices designed to
scale to multiple queues. Users configure only two knobs, the target
read and synchronous write latencies, and the scheduler tunes itself to
achieve that latency goal.

The implementation is based on "tokens", built on top of the scalable
bitmap library. Tokens serve as a mechanism for limiting requests. There
are two tiers of tokens: queueing tokens and dispatch tokens.

A queueing token is required to allocate a request. In fact, these
tokens are actually the blk-mq internal scheduler tags, but the
scheduler manages the allocation directly in order to implement its
policy.

Dispatch tokens are device-wide and split up into two scheduling
domains: reads vs. writes. Each hardware queue dispatches batches
round-robin between the scheduling domains as long as tokens are
available for that domain.

These tokens can be used as the mechanism to enable various policies.
The policy Kyber uses is inspired by active queue management techniques
for network routing, similar to blk-wbt. The scheduler monitors
latencies and scales the number of dispatch tokens accordingly. Queueing
tokens are used to prevent starvation of synchronous requests by
asynchronous requests.

Various extensions are possible, including better heuristics and ionice
support. The new scheduler isn't set as the default yet.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-04-14 14:06:58 -06:00
Christoph Hellwig
48920ff2a5 block: remove the discard_zeroes_data flag
Now that we use the proper REQ_OP_WRITE_ZEROES operation everywhere we can
kill this hack.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-04-08 11:25:38 -06:00
Shaohua Li
297e3d8547 blk-throttle: make throtl_slice tunable
throtl_slice is important for blk-throttling. It's called slice
internally but it really is a time window blk-throttling samples data.
blk-throttling will make decision based on the samplings. An example is
bandwidth measurement. A cgroup's bandwidth is measured in the time
interval of throtl_slice.

A small throtl_slice meanse cgroups have smoother throughput but burn
more CPUs. It has 100ms default value, which is not appropriate for all
disks. A fast SSD can dispatch a lot of IOs in 100ms. This patch makes
it tunable.

Since throtl_slice isn't a time slice, the sysfs name
'throttle_sample_time' reflects its character better.

Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-28 08:02:20 -06:00
Linus Torvalds
c1aac62f36 A slightly quieter cycle for documentation this time around.
Three more DocBook template files have been converted to RST; only 21 to
 go.  There are various build improvements and the usual array of
 documentation improvements and fixes.
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Merge tag 'docs-4.11' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "A slightly quieter cycle for documentation this time around.

  Three more DocBook template files have been converted to RST; only 21
  to go. There are various build improvements and the usual array of
  documentation improvements and fixes"

* tag 'docs-4.11' of git://git.lwn.net/linux: (44 commits)
  docs / driver-api: Fix structure references in device_link.rst
  PM / docs: Fix structure references in device.rst
  Add a target to check broken external links in the Documentation
  Documentation: Fix linux-api list typo
  Documentation: DocBook/Makefile comment typo
  Improve sparse documentation
  Documentation: make Makefile.sphinx no-ops quieter
  Documentation: DMA-ISA-LPC.txt
  Documentation: input: fix path to input code definitions
  docs: Remove the copyright year from conf.py
  docs: Fix a warning in the Korean HOWTO.rst translation
  PM / sleep / docs: Convert PM notifiers document to reST
  PM / core / docs: Convert sleep states API document to reST
  PM / core: Update kerneldoc comments in pm.h
  doc-rst: Fix recursive make invocation from macros
  doc-rst: Delete output of failed dot-SVG conversion
  doc-rst: Break shell command sequences on failure
  Documentation/sphinx: make targets independent of Sphinx work for HAVE_SPHINX=0
  doc-rst: fixed cleandoc target when used with O=dir
  Documentation/sphinx: prevent generation of .pyc files in the source tree
  ...
2017-02-22 18:51:29 -08:00
Masanari Iida
8da9704c8b Doc: Fix double words in Documentation
This patch fix some double words found in Documentation.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2017-01-26 15:25:41 -07:00
Jeff Moyer
7158339d4c block: fix up io_poll documentation
/sys/block/<dev>/queue/io_poll is a boolean.  Fix the docs.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-01-03 16:47:13 -07:00
Jens Axboe
80e091d10e blk-wbt: allow reset of default latency through sysfs
Allow a write of '-1' to reset the default latency target for
a given device. This removes knowledge of the different default
settings for rotational vs non-rotational from user space.

Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-28 10:27:03 -07:00
Jens Axboe
10e6246e22 block: document the 'io_poll_delay' queue sysfs file
This was documented in the original commit, 64f1c21e86, but it
never made it into the proper location for queue sysfs files.

Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-17 22:23:02 -07:00
Yasuaki Ishimatsu
92153d30c7 null_blk: add usage hints for NVM
If CONFIG_NVM is disabled, loading null_block module with use_lightnvm=1
fails. But there are no messages and documents related to the failure.

Add the appropriate error message.

Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>

Massaged the text a bit.

Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-16 08:26:11 -07:00
Jens Axboe
87760e5eef block: hook up writeback throttling
Enable throttling of buffered writeback to make it a lot
more smooth, and has way less impact on other system activity.
Background writeback should be, by definition, background
activity. The fact that we flush huge bundles of it at the time
means that it potentially has heavy impacts on foreground workloads,
which isn't ideal. We can't easily limit the sizes of writes that
we do, since that would impact file system layout in the presence
of delayed allocation. So just throttle back buffered writeback,
unless someone is waiting for it.

The algorithm for when to throttle takes its inspiration in the
CoDel networking scheduling algorithm. Like CoDel, blk-wb monitors
the minimum latencies of requests over a window of time. In that
window of time, if the minimum latency of any request exceeds a
given target, then a scale count is incremented and the queue depth
is shrunk. The next monitoring window is shrunk accordingly. Unlike
CoDel, if we hit a window that exhibits good behavior, then we
simply increment the scale count and re-calculate the limits for that
scale value. This prevents us from oscillating between a
close-to-ideal value and max all the time, instead remaining in the
windows where we get good behavior.

Unlike CoDel, blk-wb allows the scale count to to negative. This
happens if we primarily have writes going on. Unlike positive
scale counts, this doesn't change the size of the monitoring window.
When the heavy writers finish, blk-bw quickly snaps back to it's
stable state of a zero scale count.

The patch registers a sysfs entry, 'wb_lat_usec'. This sets the latency
target to me met. It defaults to 2 msec for non-rotational storage, and
75 msec for rotational storage. Setting this value to '0' disables
blk-wb. Generally, a user would not have to touch this setting.

We don't enable WBT on devices that are managed with CFQ, and have
a non-root block cgroup attached. If we have a proportional share setup
on this particular disk, then the wbt throttling will interfere with
that. We don't have a strong need for wbt for that case, since we will
rely on CFQ doing that for us.

Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-10 13:53:40 -07:00
Christoph Hellwig
a2b809672e block: replace REQ_NOIDLE with REQ_IDLE
Noidle should be the default for writes as seen by all the compounds
definitions in fs.h using it.  In fact only direct I/O really should
be using NODILE, so turn the whole flag around to get the defaults
right, which will make our life much easier especially onces the
WRITE_* defines go away.

This assumes all the existing "raw" users of REQ_SYNC for writes
want noidle behavior, which seems to be spot on from a quick audit.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-01 09:43:26 -06:00
Christoph Hellwig
ef295ecf09 block: better op and flags encoding
Now that we don't need the common flags to overflow outside the range
of a 32-bit type we can encode them the same way for both the bio and
request fields.  This in addition allows us to place the operation
first (and make some room for more ops while we're at it) and to
stop having to shift around the operation values.

In addition this allows passing around only one value in the block layer
instead of two (and eventuall also in the file systems, but we can do
that later) and thus clean up a lot of code.

Last but not least this allows decreasing the size of the cmd_flags
field in struct request to 32-bits.  Various functions passing this
value could also be updated, but I'd like to avoid the churn for now.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-10-28 08:48:16 -06:00
Christoph Hellwig
e806402130 block: split out request-only flags into a new namespace
A lot of the REQ_* flags are only used on struct requests, and only of
use to the block layer and a few drivers that dig into struct request
internals.

This patch adds a new req_flags_t rq_flags field to struct request for
them, and thus dramatically shrinks the number of common requests.  It
also removes the unfortunate situation where we have to fit the fields
from the same enum into 32 bits for struct bio and 64 bits for
struct request.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Shaun Tancheff <shaun.tancheff@seagate.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-10-28 08:45:17 -06:00
Linus Walleij
a441b0d093 block: remove remnant refs to hardsect
commit e1defc4ff0
"block: Do away with the notion of hardsect_size"
removed the notion of "hardware sector size" from
the kernel in favor of logical block size, but
references remain in comments and documentation.

Update the remaining sites mentioning hardsect.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-09-14 08:44:57 -06:00
Joe Lawrence
005411ea7e doc: update block/queue-sysfs.txt entries
Add descriptions for dax, io_poll, and write_same_max_bytes files.

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-08-11 09:37:23 -06:00
Jens Axboe
1eff9d322a block: rename bio bi_rw to bi_opf
Since commit 63a4cc2486, bio->bi_rw contains flags in the lower
portion and the op code in the higher portions. This means that
old code that relies on manually setting bi_rw is most likely
going to be broken. Instead of letting that brokeness linger,
rename the member, to force old and out-of-tree code to break
at compile time instead of at runtime.

No intended functional changes in this commit.

Signed-off-by: Jens Axboe <axboe@fb.com>
2016-08-07 14:41:02 -06:00