Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue

From	Rohit Jain <rohit.k.jain@oracle.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue
Date	2017-06-05 20:10 +0200
Message-ID	<tP4BX-6kn-7@gated-at.bofh.it> (permalink)
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On 06/02/2017 11:26 AM, Peter Zijlstra wrote:
> On Fri, Jun 02, 2017 at 11:20:20AM -0700, Rohit Jain wrote:
>> On 06/01/2017 05:37 AM, Peter Zijlstra wrote:
>>> On Thu, Jun 01, 2017 at 02:28:27PM +0200, Peter Zijlstra wrote:
>>>> On Wed, May 31, 2017 at 03:19:46PM -0700, Rohit Jain wrote:
>>>>
>>>>>>> 2) This scaled capacity is normalized and mapped into buckets.
>>>>>> Why?
>>> And its not at all clear why you'd need
>>> that to begin with.
>> Here is the problem I am trying to solve:
>>
>> The benchmark(s) have a high degree of variance when run multiple
>> times.
>>
>> We believe it is because of the scheduler not being aware of the scaled
>> down capacity of the CPUs because of IRQ/RT activity.
>>
>> This patch helps in solving the above problem. Do you have any thoughts
>> on solving this problem in any other way?
> Why does determining if a CPU's capacity is scaled down need to involve
> global data? AFAICT its a purely CPU local affair.

The global array is used to determine the threshold capacity, so
that any CPU which lies below decides that a CPU is 'running low' on
available capacity. This threshold can also be statically defined to
be a fixed fraction, but having dynamic calculation to determine the
threshold works for all benchmarks.

Did you mean we should use a static cutoff and decide whether a CPU
should be treated low on capacity and skip it during idle CPU search?

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Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue Peter Zijlstra <peterz@infradead.org> - 2017-05-30 14:30 +0200
  Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue Rohit Jain <rohit.k.jain@oracle.com> - 2017-06-01 00:20 +0200
    Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue Peter Zijlstra <peterz@infradead.org> - 2017-06-01 14:30 +0200
      Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue Peter Zijlstra <peterz@infradead.org> - 2017-06-01 14:40 +0200
        Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue Rohit Jain <rohit.k.jain@oracle.com> - 2017-06-02 20:20 +0200
          Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue Peter Zijlstra <peterz@infradead.org> - 2017-06-02 20:30 +0200
            Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue Rohit Jain <rohit.k.jain@oracle.com> - 2017-06-05 20:10 +0200

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