linux-kernel - Re: [RFC PATCH 5/6] sched/fair: Select an energy-efficient CPU on task wake-up

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: <20180325013833.GA1803@queper01-VirtualBox>
Date:   Sun, 25 Mar 2018 02:38:35 +0100
From:   Quentin Perret <quentin.perret@....com>
To:     Morten Rasmussen <morten.rasmussen@....com>
Cc:     Joel Fernandes <joelaf@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Chris Redpath <chris.redpath@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Valentin Schneider <valentin.schneider@....com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Todd Kjos <tkjos@...gle.com>
Subject: Re: [RFC PATCH 5/6] sched/fair: Select an energy-efficient CPU on
 task wake-up

On Friday 23 Mar 2018 at 16:00:59 (+0000), Morten Rasmussen wrote:
> On Thu, Mar 22, 2018 at 09:27:43AM -0700, Joel Fernandes wrote:
> > Hi,
> > 
> > On Tue, Mar 20, 2018 at 2:43 AM, Dietmar Eggemann
> > <dietmar.eggemann@....com> wrote:

[...]

> > Is it possible that before the wakeup, the task's affinity is changed
> > so that p->cpus_allowed no longer contains prev_cpu ? In that case
> > prev_energy wouldn't matter since previous CPU is no longer an option?
> 
> It is possible to wake-up with a disallowed prev_cpu. In fact
> select_idle_sibling() may happily return a disallowed cpu in that case.
> The mistake gets fixed in select_task_rq() which uses
> select_fallback_rq() to find an allowed cpu instead.
> 
> Could we fix the issue in find_energy_efficient_cpu() by a simple test
> like below
> 
> if (cpumask_test_cpu(prev_cpu, &p->cpus_allowed))
> 	prev_energy = best_energy = compute_energy(p, prev_cpu);
> else
> 	prev_energy = best_energy = ULONG_MAX;

Right, that should work. I'll change this in v2.

Thanks,
Quentin