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

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On Thu, Aug 27, 2015 at 05:09:21PM +0200, Thomas Gleixner wrote:
> On Thu, 27 Aug 2015, Steven Rostedt wrote:
> > On Thu, 27 Aug 2015 15:18:49 +0200
> > Frederic Weisbecker <fweisbec@gmail.com> wrote:
> > 
> > > On Wed, Aug 26, 2015 at 04:45:44PM -0700, Hideaki Kimura wrote:
> > > > I totally agree that this is not a perfect solution. If there are 10x more
> > > > cores and sockets, just the atomic fetch_add might be too expensive.
> > > > 
> > > > However, it's comparatively/realistically the best thing we can do without
> > > > any drawbacks. We can't magically force all library developers to write the
> > > > most scalable code always.
> > > > 
> > > > My point is: this is a safety net, and a very effective one.
> > > 
> > > I mean the problem here is that a library uses an unscalable profiling feature,
> > > unconditionally as soon as you load it without even initializing anything. And
> > > this library is used in production.
> > > 
> > > At first sight, fixing that in the kernel is only a hack that just reduces a bit
> > > the symptoms.
> > > 
> > > What is the technical issue that prevents from fixing that in the library itself?
> > > Posix timers can be attached anytime.
> > 
> > I'm curious to what the downside of this patch set is? If we can fix a
> > problem that should be fixed in userspace, but does not harm the kernel
> > by doing so, is that bad? (an argument for kdbus? ;-)
> 
> The patches are not fixing a problem which should be fixed in user
> space. They merily avoid lock contention which happens to be prominent
> with that particular library. But avoiding lock contention even for 2
> threads is a worthwhile exercise if it does not hurt otherwise. And I
> can't see anything what hurts with these patches.

Sure it shouldn't really hurt anyway, since the presense of elapsing timers
itself is checked locklessly.
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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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