linux-kernel - Re: [PATCH] sched/deadline: Reduce rq lock contention in dl_add_task_root

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 for Android: free password hash cracker in your pocket

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

Message-ID: <YCE//6RaVyPzWO4W@hirez.programming.kicks-ass.net>
Date:   Mon, 8 Feb 2021 14:43:27 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Quentin Perret <qperret@...gle.com>,
        Valentin Schneider <valentin.schneider@....com>
Subject: Re: [PATCH] sched/deadline: Reduce rq lock contention in
 dl_add_task_root_domain()

On Tue, Jan 19, 2021 at 09:35:42AM +0100, Dietmar Eggemann wrote:
> dl_add_task_root_domain() is called during sched domain rebuild:
> 
>   rebuild_sched_domains_locked()
>     partition_and_rebuild_sched_domains()
>       rebuild_root_domains()
>          for all top_cpuset descendants:
>            update_tasks_root_domain()
>              for all tasks of cpuset:
>                dl_add_task_root_domain()
> 
> Change it so that only the task pi lock is taken to check if the task
> has a SCHED_DEADLINE (DL) policy. In case that p is a DL task take the
> rq lock as well to be able to safely de-reference root domain's DL
> bandwidth structure.
> 
> Most of the tasks will have another policy (namely SCHED_NORMAL) and
> can now bail without taking the rq lock.
> 
> One thing to note here: Even in case that there aren't any DL user
> tasks, a slow frequency switching system with cpufreq gov schedutil has
> a DL task (sugov) per frequency domain running which participates in DL
> bandwidth management.
> 
> Reviewed-by: Quentin Perret <qperret@...gle.com>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>

Thanks!