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Some systems benefit from completions always being steered to the strict requester cpu rather than the looser "per-socket" steering that blk_cpu_to_group() attempts by default. This is because the first CPU in the group mask ends up being completely overloaded with work, while the others (including the original submitter) has power left to spare. Allow the strict mode to be set by writing '2' to the sysfs control file. This is identical to the scheme used for the nomerges file, where '2' is a more aggressive setting than just being turned on. echo 2 > /sys/block/<bdev>/queue/rq_affinity Cc: Christoph Hellwig <hch@infradead.org> Cc: Roland Dreier <roland@purestorage.com> Tested-by: Dave Jiang <dave.jiang@intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
68 lines
2.5 KiB
Plaintext
68 lines
2.5 KiB
Plaintext
Queue sysfs files
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=================
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This text file will detail the queue files that are located in the sysfs tree
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for each block device. Note that stacked devices typically do not export
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any settings, since their queue merely functions are a remapping target.
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These files are the ones found in the /sys/block/xxx/queue/ directory.
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Files denoted with a RO postfix are readonly and the RW postfix means
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read-write.
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hw_sector_size (RO)
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-------------------
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This is the hardware sector size of the device, in bytes.
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max_hw_sectors_kb (RO)
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----------------------
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This is the maximum number of kilobytes supported in a single data transfer.
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max_sectors_kb (RW)
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-------------------
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This is the maximum number of kilobytes that the block layer will allow
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for a filesystem request. Must be smaller than or equal to the maximum
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size allowed by the hardware.
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nomerges (RW)
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-------------
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This enables the user to disable the lookup logic involved with IO
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merging requests in the block layer. By default (0) all merges are
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enabled. When set to 1 only simple one-hit merges will be tried. When
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set to 2 no merge algorithms will be tried (including one-hit or more
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complex tree/hash lookups).
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nr_requests (RW)
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----------------
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This controls how many requests may be allocated in the block layer for
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read or write requests. Note that the total allocated number may be twice
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this amount, since it applies only to reads or writes (not the accumulated
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sum).
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read_ahead_kb (RW)
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------------------
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Maximum number of kilobytes to read-ahead for filesystems on this block
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device.
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rq_affinity (RW)
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----------------
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If this option is '1', the block layer will migrate request completions to the
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cpu "group" that originally submitted the request. For some workloads this
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provides a significant reduction in CPU cycles due to caching effects.
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For storage configurations that need to maximize distribution of completion
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processing setting this option to '2' forces the completion to run on the
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requesting cpu (bypassing the "group" aggregation logic).
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scheduler (RW)
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--------------
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When read, this file will display the current and available IO schedulers
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for this block device. The currently active IO scheduler will be enclosed
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in [] brackets. Writing an IO scheduler name to this file will switch
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control of this block device to that new IO scheduler. Note that writing
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an IO scheduler name to this file will attempt to load that IO scheduler
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module, if it isn't already present in the system.
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Jens Axboe <jens.axboe@oracle.com>, February 2009
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