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When a single-threaded process has a non-local mm_cpumask, try to use that point to flush the TLBs out of other CPUs in the cpumask. An IPI is used for clearing remote CPUs for a few reasons: - An IPI can end lazy TLB use of the mm, which is required to prevent TLB entries being created on the remote CPU. The alternative is to drop lazy TLB switching completely, which costs 7.5% in a context switch ping-pong test betwee a process and kernel idle thread. - An IPI can have remote CPUs flush the entire PID, but the local CPU can flush a specific VA. tlbie would require over-flushing of the local CPU (where the process is running). - A single threaded process that is migrated to a different CPU is likely to have a relatively small mm_cpumask, so IPI is reasonable. No other thread can concurrently switch to this mm, because it must have been given a reference to mm_users by the current thread before it can use_mm. mm_users can be asynchronously incremented (by mm_activate or mmget_not_zero), but those users must use remote mm access and can't use_mm or access user address space. Existing code makes the this assumption already, for example sparc64 has reset mm_cpumask using this condition since the start of history, see arch/sparc/kernel/smp_64.c. This reduces tlbies for a kernel compile workload from 0.90M to 0.12M, tlbiels are increased significantly due to the PID flushing for the cleaning up remote CPUs, and increased local flushes (PID flushes take 128 tlbiels vs 1 tlbie). Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
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| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.