linux-kernel - Re: [PATCH 2/2] sched/fair: Relax task

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87tuo6lg39.mognet@arm.com>
Date:   Fri, 16 Apr 2021 10:43:38 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Rik van Riel <riel@...riel.com>, linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Qais Yousef <qais.yousef@....com>,
        Quentin Perret <qperret@...gle.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Lingutla Chandrasekhar <clingutla@...eaurora.org>
Subject: Re: [PATCH 2/2] sched/fair: Relax task_hot() for misfit tasks

On 15/04/21 16:39, Rik van Riel wrote:
> On Thu, 2021-04-15 at 18:58 +0100, Valentin Schneider wrote:
>> Consider the following topology:
>>
>> Long story short, preempted misfit tasks are affected by task_hot(),
>> while
>> currently running misfit tasks are intentionally preempted by the
>> stopper
>> task to migrate them over to a higher-capacity CPU.
>>
>> Align detach_tasks() with the active-balance logic and let it pick a
>> cache-hot misfit task when the destination CPU can provide a capacity
>> uplift.
>>
>> Signed-off-by: Valentin Schneider <valentin.schneider@....com>
>
> Reviewed-by: Rik van Riel <riel@...riel.com>
>

Thanks!

>
> This patch looks good, but...
>
>> @@ -7672,6 +7698,15 @@ int can_migrate_task(struct task_struct *p,
>> struct lb_env *env)
>>      if (tsk_cache_hot == -1)
>>              tsk_cache_hot = task_hot(p, env);
>>
>> +	/*
>> +	 * On a (sane) asymmetric CPU capacity system, the increase in
>> compute
>> +	 * capacity should offset any potential performance hit caused
>> by a
>> +	 * migration.
>> +	 */
>> +	if ((env->dst_grp_type == group_has_spare) &&
>> +	    !migrate_degrades_capacity(p, env))
>> +		tsk_cache_hot = 0;
>
> ... I'm starting to wonder if we should not rename the
> tsk_cache_hot variable to something else to make this
> code more readable. Probably in another patch :)
>

I'd tend to agree, but naming is hard. "migration_harmful" ?

> --
> All Rights Reversed.