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Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper functions

From Tejun Heo <tj@kernel.org>
Newsgroups linux.kernel
Subject Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper functions
Date 2016-04-07 21:00 +0200
Message-ID <rlnjS-8fc-63@gated-at.bofh.it> (permalink)
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Hello, Waiman.

On Thu, Apr 07, 2016 at 02:52:33PM -0400, Waiman Long wrote:
> As long as atomic reset is an optional feature that caller can choose at
> init time, I am OK to provide this functionality. I just don't want it to be
> the default because of the performance overhead.

Please take a look at how percpu-ref coordinates global
synchronization.  The hot path overhead is one branch which is
extremely easy to predict and shouldn't show up anywhere.  If you're
gonna provide reset at all (which btw always kinda baffles me, what's
wrong with taking a snapshot value and taking delta from there?), you
need to make it actually work reliably.

Thanks.

-- 
tejun

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Thread

Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper  functions Tejun Heo <tj@kernel.org> - 2016-04-04 18:10 +0200
  Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper  functions Waiman Long <waiman.long@hpe.com> - 2016-04-06 22:10 +0200
  Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper  functions Waiman Long <waiman.long@hpe.com> - 2016-04-07 00:00 +0200
    Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper  functions Tejun Heo <tj@kernel.org> - 2016-04-07 01:00 +0200
      Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper  functions Waiman Long <waiman.long@hpe.com> - 2016-04-07 18:00 +0200
        Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper  functions Tejun Heo <tj@kernel.org> - 2016-04-07 18:10 +0200
          Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper  functions Tejun Heo <tj@kernel.org> - 2016-04-07 21:00 +0200
            Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper  functions Waiman Long <waiman.long@hpe.com> - 2016-04-07 22:40 +0200
              Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper  functions Tejun Heo <tj@kernel.org> - 2016-04-07 22:50 +0200
                Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper  functions Waiman Long <waiman.long@hpe.com> - 2016-04-07 23:40 +0200
          Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper  functions Waiman Long <waiman.long@hpe.com> - 2016-04-07 21:10 +0200

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