diff options
| author | Ingo Molnar <mingo@elte.hu> | 2007-01-23 10:45:50 +0100 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-01-23 11:08:03 -0800 |
| commit | 1b5180b65122666a36a1a232b7b9b38b21a9dcdd (patch) | |
| tree | a61b7cea4cd410755bd5f87ea886554ad1d05676 /drivers/usb/serial/funsoft.c | |
| parent | b53d0b919ebe227e2b8e49b6e0ddee506be83aa8 (diff) | |
[PATCH] notifiers: fix blocking_notifier_call_chain() scalability
while lock-profiling the -rt kernel i noticed weird contention during
mmap-intense workloads, and the tracer showed the following gem, in one
of our MM hotpaths:
threaded-2771 1.... 65us : sys_munmap (sysenter_do_call)
threaded-2771 1.... 66us : profile_munmap (sys_munmap)
threaded-2771 1.... 66us : blocking_notifier_call_chain (profile_munmap)
threaded-2771 1.... 66us : rt_down_read (blocking_notifier_call_chain)
ouch! a global rw-semaphore taken in one of the most performance-
sensitive codepaths of the kernel. And i dont even have oprofile
enabled! All distro kernels have CONFIG_PROFILING enabled, so this
scalability problem affects the majority of Linux users.
The fix is to enhance blocking_notifier_call_chain() to only take the
lock if there appears to be work on the call-chain.
With this patch applied i get nicely saturated system, and much higher
munmap performance, on SMP systems.
And as a bonus this also fixes a similar scalability bottleneck in the
thread-exit codepath: profile_task_exit() ...
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/usb/serial/funsoft.c')
0 files changed, 0 insertions, 0 deletions