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Re: [PATCH 0/3] timer: Improve itimers scalability

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Hi Andrew,

On Tue, 2015-08-25 at 20:27 -0700, Andrew Morton wrote:
> On Tue, 25 Aug 2015 20:17:45 -0700 Jason Low <jason.low2@hp.com> wrote:
> 
> > When running a database workload on a 16 socket machine, there were
> > scalability issues related to itimers.
> > 
> > Commit 1018016c706f addressed the issue with the thread_group_cputimer
> > spinlock taking up a significant portion of total run time.
> > 
> > This patch series address the other issue where a lot of time is spent
> > trying to acquire the sighand lock. It was found in some cases that
> > 200+ threads were simultaneously contending for the same sighand lock,
> > reducing throughput by more than 30%.
> 
> Does this imply that the patchset increased the throughput of this
> workload by 30%?
> 
> And is this test case realistic?  If not, what are the benefits on a
> real-world workload?

Yes, the test case with the database workload is realistic. We did write
a simple micro-benchmark that just generates the contention in this code
path to quickly test experimental patches, since the database takes
longer to set up and run. However, the performance issues and numbers
mentioned here are for the database workload.

These patches should also be beneficial for other multi-threaded
applications which uses process-wide timers particularly on systems with
a lot of cores.

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[PATCH 0/3] timer: Improve itimers scalability Jason Low <jason.low2@hp.com> - 2015-08-26 05:20 +0200
  [PATCH 2/3] timer: Check thread timers only when there are active thread timers Jason Low <jason.low2@hp.com> - 2015-08-26 05:20 +0200
  [PATCH 1/3] timer: Optimize fastpath_timer_check() Jason Low <jason.low2@hp.com> - 2015-08-26 05:20 +0200
    Re: [PATCH 1/3] timer: Optimize fastpath_timer_check() Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 00:00 +0200
    Re: [PATCH 1/3] timer: Optimize fastpath_timer_check() Davidlohr Bueso <dave@stgolabs.net> - 2015-08-31 17:20 +0200
      Re: [PATCH 1/3] timer: Optimize fastpath_timer_check() Jason Low <jason.low2@hp.com> - 2015-08-31 21:50 +0200
  [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Jason Low <jason.low2@hp.com> - 2015-08-26 05:20 +0200
    Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-26 20:00 +0200
      Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 00:40 +0200
        Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Jason Low <jason.low2@hp.com> - 2015-08-27 01:00 +0200
    Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 01:00 +0200
      Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Jason Low <jason.low2@hp.com> - 2015-08-27 01:40 +0200
        Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Jason Low <jason.low2@hp.com> - 2015-08-27 07:00 +0200
        Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 15:00 +0200
          Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Jason Low <jason.low2@hp.com> - 2015-08-27 22:40 +0200
            Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 23:20 +0200
  Re: [PATCH 0/3] timer: Improve itimers scalability Andrew Morton <akpm@linux-foundation.org> - 2015-08-26 05:30 +0200
    Re: [PATCH 0/3] timer: Improve itimers scalability Jason Low <jason.low2@hp.com> - 2015-08-26 18:40 +0200
      Re: [PATCH 0/3] timer: Improve itimers scalability Oleg Nesterov <oleg@redhat.com> - 2015-08-26 19:20 +0200
        Re: [PATCH 0/3] timer: Improve itimers scalability Jason Low <jason.low2@hp.com> - 2015-08-27 00:10 +0200
          Re: [PATCH 0/3] timer: Improve itimers scalability Hideaki Kimura <hideaki.kimura@hpe.com> - 2015-08-27 01:20 +0200
            Re: [PATCH 0/3] timer: Improve itimers scalability Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 01:20 +0200
              Re: [PATCH 0/3] timer: Improve itimers scalability Hideaki Kimura <hideaki.kimura@hpe.com> - 2015-08-27 02:00 +0200
                Re: [PATCH 0/3] timer: Improve itimers scalability Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 15:20 +0200
                Re: [PATCH 0/3] timer: Improve itimers scalability Steven Rostedt <rostedt@goodmis.org> - 2015-08-27 16:50 +0200
                Re: [PATCH 0/3] timer: Improve itimers scalability Thomas Gleixner <tglx@linutronix.de> - 2015-08-27 17:20 +0200
                Re: [PATCH 0/3] timer: Improve itimers scalability Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 17:20 +0200

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