linux-kernel - Re: [RFC 0/2] Optimize the idle CPU search

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Date:   Tue, 9 Jul 2019 12:18:47 +0530
From:   Subhra Mazumdar <subhra.mazumdar@...cle.com>
To:     Parth Shah <parth@...ux.ibm.com>, linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...hat.com, vincent.guittot@...aro.org
Subject: Re: [RFC 0/2] Optimize the idle CPU search


On 7/9/19 11:08 AM, Parth Shah wrote:
>
> On 7/9/19 5:38 AM, Subhra Mazumdar wrote:
>> On 7/8/19 10:24 AM, Parth Shah wrote:
>>> When searching for an idle_sibling, scheduler first iterates to search for
>>> an idle core and then for an idle CPU. By maintaining the idle CPU mask
>>> while iterating through idle cores, we can mark non-idle CPUs for which
>>> idle CPU search would not have to iterate through again. This is especially
>>> true in a moderately load system
>>>
>>> Optimize idle CPUs search by marking already found non idle CPUs during
>>> idle core search. This reduces iteration count when searching for idle
>>> CPUs, resulting in lower iteration count.
>>>
>> I believe this can co-exist with latency-nice? We can derive the 'nr' in
>> select_idle_cpu from latency-nice and use the new mask to iterate.
>>
> I agree, can be done with latency-nice.
>
> Maybe something like below?
> smt = nr_cpus / nr_cores
> nr = smt + (p->latency_nice * (total_cpus-smt) / max_latency_nice)
>
> This limits lower bounds to 1 core and goes through all the cores if
> latency_nice is maximum for a task.
Yes I had similar in mind.