From: Rohit Jain <rohit.k.jain@oracle.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com,
vincent.guittot@linaro.org, morten.rasmussen@arm.com,
dietmar.eggemann@arm.com
Subject: Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue
Date: Wed, 31 May 2017 15:19:46 -0700 [thread overview]
Message-ID: <63736e6f-37e6-e287-a920-56ab0d0586b7@oracle.com> (raw)
In-Reply-To: <20170530122831.5fyywtplq4jawj3j@hirez.programming.kicks-ass.net>
On 05/30/2017 05:28 AM, Peter Zijlstra wrote:
> On Mon, May 22, 2017 at 01:48:14PM -0700, Rohit Jain wrote:
>> The patch introduces capacity awarness in scheduler (CAS) which avoids
>> CPUs which might have their capacities reduced (due to IRQ/RT activity)
>> when trying to schedule threads (on the push side) in the system. This
>> awareness has been added into the fair scheduling class.
>>
>> It does so by, using the following algorithm:
>> --------------------------------------------------------------------------
>> 1) As in rt_avg the scaled capacities are already calculated.
>>
>> 2) This scaled capacity is normalized and mapped into buckets.
> Why?
This is done to deterministically define the CPUs which are low on
capacities. By mapping it into buckets it becomes easier to do a
percentile calculation.
>> 3) Any CPU which lies below the 80th percentile in terms of percentage
>> capacity available is considered as a low capacity CPU.
> Random number; can we do better? What does existing code do?
>
Existing code checks to see if the waker is running on a CPU with better
capacity than the 'previous cpu'. If that is the case the waker cpu is
provided as 'target' to select_idle_sibling. (When I say capacity this
is not the scaled one because of IRQ, RT, etc.)
However, in case this 'target' is not an idle CPU, the rest of
select_idle_sibling would ignore the capacities altogether.
next prev parent reply other threads:[~2017-05-31 22:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-22 20:48 [PATCH] sched: Introduce scaled capacity awareness in enqueue Rohit Jain
2017-05-30 12:28 ` Peter Zijlstra
2017-05-31 22:19 ` Rohit Jain [this message]
2017-06-01 12:28 ` Peter Zijlstra
2017-06-01 12:37 ` Peter Zijlstra
2017-06-02 18:20 ` Rohit Jain
2017-06-02 18:26 ` Peter Zijlstra
2017-06-05 18:08 ` Rohit Jain
2017-06-12 15:36 ` Peter Zijlstra
2017-06-13 0:31 ` Rohit Jain
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