linux-kernel - Re: [PATCH 1/4] sched: consolidate and cleanup access to CPU's max compute capacity

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: <be527eb1-d253-b9fe-ecc9-4c7b04da9efd@arm.com>
Date:   Thu, 14 Sep 2023 22:45:46 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, sudeep.holla@....com,
        gregkh@...uxfoundation.org, rafael@...nel.org, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, viresh.kumar@...aro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-pm@...r.kernel.org
Cc:     conor.dooley@...rochip.com, suagrfillet@...il.com,
        ajones@...tanamicro.com, lftan@...nel.org
Subject: Re: [PATCH 1/4] sched: consolidate and cleanup access to CPU's max
 compute capacity

On 01/09/2023 15:03, Vincent Guittot wrote:
> Remove struct rq cpu_capacity_orig field and use arch_scale_cpu_capacity()
> instead.
> 
> Scheduler uses 3 methods to get access to the CPU's max compute capacity:
> - arch_scale_cpu_capacity(cpu) which is the default way to get CPU's capacity.
> - cpu_capacity_orig field which is periodically updated with
>   arch_scale_cpu_capacity().
> - capacity_orig_of(cpu) which encapsulates rq->cpu_capacity_orig
> 
> There is no real need to save the value returned by arch_scale_cpu_capacity()
> in struct rq. arch_scale_cpu_capacity() returns:
> - either a per_cpu variable.
> - or a const value for systems which have only one capacity.
> 
> Remove cpu_capacity_orig and use arch_scale_cpu_capacity() everywhere.
> 
> No functional changes.
> 
> some tests of Arm64:
> small SMP device (hikey): no noticeable changes
> HMP device (RB5): hackbench shows minor improvement (1-2%)
> large smp (thx2): hackbench and tbench shows minor improvement (1%)
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>

Next to util_fits_cpu() which uses capacity_orig as a local variable
(which is fine) there is sis() referring to capacity_orig in a comment.

Documentation/scheduler/sched-capacity.rst uses the term `capacity_orig`
in chapter 1.2 to explain the difference between CPU's maximum
(attainable) capacity and capacity as the former reduced by pressure.

Not sure if you want to change those refs as well with this patch?
People might get confused about the term `capacity_orig` pretty soon.

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>