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Waiman Long c7be96af89 signals: avoid unnecessary taking of sighand->siglock
When running certain database workload on a high-end system with many
CPUs, it was found that spinlock contention in the sigprocmask syscalls
became a significant portion of the overall CPU cycles as shown below.

  9.30%  9.30%  905387  dataserver  /proc/kcore 0x7fff8163f4d2
  [k] _raw_spin_lock_irq
            |
            ---_raw_spin_lock_irq
               |
               |--99.34%-- __set_current_blocked
               |          sigprocmask
               |          sys_rt_sigprocmask
               |          system_call_fastpath
               |          |
               |          |--50.63%-- __swapcontext
               |          |          |
               |          |          |--99.91%-- upsleepgeneric
               |          |
               |          |--49.36%-- __setcontext
               |          |          ktskRun

Looking further into the swapcontext function in glibc, it was found that
the function always call sigprocmask() without checking if there are
changes in the signal mask.

A check was added to the __set_current_blocked() function to avoid taking
the sighand->siglock spinlock if there is no change in the signal mask.
This will prevent unneeded spinlock contention when many threads are
trying to call sigprocmask().

With this patch applied, the spinlock contention in sigprocmask() was
gone.

Link: http://lkml.kernel.org/r/1474979209-11867-1-git-send-email-Waiman.Long@hpe.com
Signed-off-by: Waiman Long <Waiman.Long@hpe.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Stas Sergeev <stsp@list.ru>
Cc: Scott J Norton <scott.norton@hpe.com>
Cc: Douglas Hatch <doug.hatch@hpe.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-12-14 16:04:07 -08:00
arch arm64 updates for 4.10: 2016-12-13 16:39:21 -08:00
block SCSI misc on 20161213 2016-12-14 10:49:33 -08:00
certs certs: Add a secondary system keyring that can be added to dynamically 2016-04-11 22:48:09 +01:00
crypto Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2016-12-10 16:21:55 -05:00
Documentation . various fixes and improvements to request-based DM and DM multipath 2016-12-14 11:01:00 -08:00
drivers . various fixes and improvements to request-based DM and DM multipath 2016-12-14 11:01:00 -08:00
firmware WHENCE: use https://linuxtv.org for LinuxTV URLs 2015-12-04 10:35:11 -02:00
fs btrfs: better handle btrfs_printk() defaults 2016-12-14 16:04:07 -08:00
include signals: avoid unnecessary taking of sighand->siglock 2016-12-14 16:04:07 -08:00
init Merge branch 'for-4.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq 2016-12-13 12:59:57 -08:00
ipc sched/wake_q: Rename WAKE_Q to DEFINE_WAKE_Q 2016-11-21 10:29:01 +01:00
kernel signals: avoid unnecessary taking of sighand->siglock 2016-12-14 16:04:07 -08:00
lib Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/shli/md 2016-12-14 10:58:17 -08:00
mm mm, compaction: allow compaction for GFP_NOFS requests 2016-12-14 16:04:07 -08:00
net Merge branch 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-12-12 19:25:04 -08:00
samples VFIO updates for v4.10-rc1 2016-12-13 09:23:56 -08:00
scripts Char/Misc driver patches for 4.10-rc1 2016-12-13 12:11:01 -08:00
security Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-12-12 19:56:15 -08:00
sound Main pull request for drm for 4.10 kernel 2016-12-13 09:35:09 -08:00
tools arm64 updates for 4.10: 2016-12-13 16:39:21 -08:00
usr usr/Kconfig: make initrd compression algorithm selection not expert 2014-12-13 12:42:52 -08:00
virt Small release, the most interesting stuff is x86 nested virt improvements. 2016-12-13 15:47:02 -08:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Merge branch 'misc' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild 2016-08-02 16:48:52 -04:00
.mailmap Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2016-10-15 09:26:12 -07:00
COPYING
CREDITS Merge branch 'x86-microcode-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-12-12 15:23:02 -08:00
Kbuild scripts/gdb: provide linux constants 2016-05-23 17:04:14 -07:00
Kconfig
MAINTAINERS SCSI misc on 20161213 2016-12-14 10:49:33 -08:00
Makefile Linux 4.9 2016-12-11 11:17:54 -08:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

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.