Re: [RFC,v2 1/3] sched: set loop_max after rq lock is taken

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [RFC,v2 1/3] sched: set loop_max after rq lock is taken
Date	2017-02-09 14:40 +0100
Message-ID	<t8X75-6JS-41@gated-at.bofh.it> (permalink)
References	<t8wgy-6w4-11@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wed, Feb 08, 2017 at 09:43:27AM +0100, Uladzislau Rezki wrote:
> From: Uladzislau 2 Rezki <uladzislau2.rezki@sonymobile.com>
> 
> While doing a load balance there is a race in setting
> loop_max variable since nr_running can be changed causing
> incorect iteration loops.
> 
> As a result we may skip some candidates or check the same
> tasks again.

When doing the actual migration we'll drop this lock again and
nr_running can change again.

This cannot be done perfectly, all of load-balancing is riddled with
races like this, nobody cares.

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[RFC,v2 1/3] sched: set loop_max after rq lock is taken Uladzislau Rezki <urezki@gmail.com> - 2017-02-08 10:00 +0100
  [RFC,v2 3/3] sched: ignore task_h_load for CPU_NEWLY_IDLE Uladzislau Rezki <urezki@gmail.com> - 2017-02-08 10:00 +0100
    Re: [RFC,v2 3/3] sched: ignore task_h_load for CPU_NEWLY_IDLE Mike Galbraith <efault@gmx.de> - 2017-02-08 10:50 +0100
      Re: [RFC,v2 3/3] sched: ignore task_h_load for CPU_NEWLY_IDLE Uladzislau Rezki <urezki@gmail.com> - 2017-02-09 11:20 +0100
    Re: [RFC,v2 3/3] sched: ignore task_h_load for CPU_NEWLY_IDLE Peter Zijlstra <peterz@infradead.org> - 2017-02-09 13:30 +0100
      Re: [RFC,v2 3/3] sched: ignore task_h_load for CPU_NEWLY_IDLE Uladzislau Rezki <urezki@gmail.com> - 2017-02-09 20:10 +0100
        Re: [RFC,v2 3/3] sched: ignore task_h_load for CPU_NEWLY_IDLE Peter Zijlstra <peterz@infradead.org> - 2017-02-13 15:00 +0100
          Re: [RFC,v2 3/3] sched: ignore task_h_load for CPU_NEWLY_IDLE Uladzislau Rezki <urezki@gmail.com> - 2017-02-13 18:20 +0100
  Re: [RFC,v2 1/3] sched: set loop_max after rq lock is taken Peter Zijlstra <peterz@infradead.org> - 2017-02-09 14:40 +0100

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