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Re: [PATCH 0/8] sched/deadline: Return the best satisfying affinity and dl in cpudl_find

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Hi,

On 23/03/17 19:32, Byungchul Park wrote:
> cpudl_find() is used to find a cpu having the latest dl. The function
> should return the latest cpu among ones satisfying task's affinity and
> dl constraint, but current code gives up immediately and just return
> fail when it fails at the test *only with* the maximum cpu.
> 
> For example:
> 
>    cpu 0 is running a task (dl: 10).
>    cpu 1 is running a task (dl: 9).
>    cpu 2 is running a task (dl: 8).
>    cpu 3 is running a task (dl: 2).
> 
>    where cpu 3 want to push a task (affinity is 1 2 3 and dl is 1).

Hummm, but this should only happen if you disable admission control,
right? Otherwise task's affinity can't be smaller that 0-3.

> 
> In this case, the task should be migrated from cpu 3 to cpu 1, and
> preempt cpu 1's task. However, current code just returns fail because
> it fails at the affinity test with the maximum cpu, that is, cpu 0.
> 
> This patch set tries to find the best among ones satisfying task's
> affinity and dl constraint until success or no more to see.
> 

Anyway, do you have numbers showing how common is you fail scenario?
It would be interesting to understand how much the slow path is actually
used, IMHO.

Thanks,

- Juri

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[PATCH 0/8] sched/deadline: Return the best satisfying affinity and dl in cpudl_find Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
  [PATCH 4/8] sched/deadline: Factor out the selecting of suitable max cpu Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
  [PATCH 3/8] sched/deadline: Add cpudl_maximum_dl() for clean-up Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
  [PATCH 5/8] sched/deadline: Protect read of cpudl heap with a lock Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
  [PATCH 2/8] sched/deadline: Re-define parameters of cpudl heapify functions Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
  [PATCH 6/8] sched/deadline: Don't return meaningless cpu in cpudl_maximum_cpu() Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
  [PATCH 7/8] sched/deadline: Factor out the modifying of cpudl's heap tree Byungchul Park <byungchul.park@lge.com> - 2017-03-23 11:40 +0100
  Re: [PATCH 0/8] sched/deadline: Return the best satisfying affinity  and dl in cpudl_find Byungchul Park <byungchul.park@lge.com> - 2017-03-23 23:40 +0100
  Re: [PATCH 0/8] sched/deadline: Return the best satisfying affinity  and dl in cpudl_find Juri Lelli <juri.lelli@arm.com> - 2017-03-27 16:10 +0200
    Re: [PATCH 0/8] sched/deadline: Return the best satisfying affinity  and dl in cpudl_find Byungchul Park <byungchul.park@lge.com> - 2017-03-28 02:50 +0200
      Re: [PATCH 0/8] sched/deadline: Return the best satisfying affinity  and dl in cpudl_find Juri Lelli <juri.lelli@arm.com> - 2017-03-28 09:20 +0200
        Re: [PATCH 0/8] sched/deadline: Return the best satisfying affinity  and dl in cpudl_find Byungchul Park <byungchul.park@lge.com> - 2017-03-28 09:40 +0200

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