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Re: [PATCH 0/4] block: account io: kill atomic operations

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On 07/16/2015 08:59 AM, Tejun Heo wrote:
> On Thu, Jul 16, 2015 at 08:48:41AM -0600, Jens Axboe wrote:
>> I've played with this before, but always ran into the hurdle of making
>> part_in_flight() too expensive ended up hurting results in the end. Making
>> the inc/dec parts of accounting percpu is a no-brainer, unfortunately the
>> summing then becomes pretty expensive. I'll run this through some testing
>> and see what kind of results I get.
>
> The only place which could be a problem is part_round_stats() and we
> can do that *way* lazier.  I don't think we're using that internally.
> Why are we even invoking it from IO issue / completion path?

Right, that's where it's called in the fast path. Right now, it's 
per-jiffy lazy. As to how/when it's called, I don't believe that has 
changed since those stats were introduced. If we can move that out of 
the fast path, then the percpu changes are straight forward.

-- 
Jens Axboe

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[PATCH 0/4] block: account io: kill atomic operations Ming Lei <tom.leiming@gmail.com> - 2015-07-16 05:20 +0200
  [PATCH 3/4] block: partition: introduce 'cpu' para to part_inc|dec_in_flight Ming Lei <tom.leiming@gmail.com> - 2015-07-16 05:30 +0200
  [PATCH 1/4] block: partition: introduce hd_free_part() Ming Lei <tom.leiming@gmail.com> - 2015-07-16 05:30 +0200
  [PATCH 2/4] block: partition: convert percpu ref Ming Lei <tom.leiming@gmail.com> - 2015-07-16 05:30 +0200
    Re: [PATCH 2/4] block: partition: convert percpu ref Tejun Heo <tj@kernel.org> - 2015-07-16 16:40 +0200
  [PATCH 4/4] block: account io: convert part->in_fligh[] into percpu variable Ming Lei <tom.leiming@gmail.com> - 2015-07-16 05:30 +0200
    Re: [PATCH 4/4] block: account io: convert part->in_fligh[] into  percpu variable Tejun Heo <tj@kernel.org> - 2015-07-16 16:50 +0200
  Re: [PATCH 0/4] block: account io: kill atomic operations Jens Axboe <axboe@kernel.dk> - 2015-07-16 16:50 +0200
    Re: [PATCH 0/4] block: account io: kill atomic operations Tejun Heo <tj@kernel.org> - 2015-07-16 17:00 +0200
      Re: [PATCH 0/4] block: account io: kill atomic operations Jens Axboe <axboe@kernel.dk> - 2015-07-16 17:10 +0200
    Re: [PATCH 0/4] block: account io: kill atomic operations Jens Axboe <axboe@kernel.dk> - 2015-07-16 17:10 +0200
    Re: [PATCH 0/4] block: account io: kill atomic operations Ming Lei <tom.leiming@gmail.com> - 2015-07-16 17:10 +0200

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