linux-kernel - Re: [PATCH] sched/idle: Prevent stopping the tick when there is no cpuidle driver

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: <fe5038e1-e06b-41dd-9584-cbd992bef1fe@arm.com>
Date: Mon, 15 Jan 2024 13:40:54 +0100
From: Pierre Gondois <pierre.gondois@....com>
To: Thomas Gleixner <tglx@...utronix.de>,
 Anna-Maria Behnsen <anna-maria@...utronix.de>, linux-kernel@...r.kernel.org
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Daniel Bristot de Oliveira
 <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>
Subject: Re: [PATCH] sched/idle: Prevent stopping the tick when there is no
 cpuidle driver

Hello Thomas,

On 1/12/24 15:52, Thomas Gleixner wrote:
> On Fri, Jan 12 2024 at 14:39, Pierre Gondois wrote:
>> On 1/12/24 11:56, Anna-Maria Behnsen wrote:
>>> Pierre Gondois <pierre.gondois@....com> writes:
>>>> I agree that the absence of cpuidle driver prevents from reaching deep
>>>> idle states. FWIU, there is however still benefits in stopping the tick
>>>> on such platform.
>>>
>>> What's the benefit?
>>
>> I did the following test:
>> - on an arm64 Juno-r2 platform (2 big A-72 and 4 little A-53 CPUs)
>> - booting with 'cpuidle.off=1'
>> - using the energy counters of the platforms
>>     (the counters measure energy for the whole cluster of big/little CPUs)
>> - letting the platform idling during 10s
>>
>> So the energy consumption would be up:
>> - ~6% for the big CPUs
>> - ~10% for the litte CPUs
> 
> Fair enough, but what's the actual usecase?
> 
> NOHZ w/o cpuidle driver seems a rather academic exercise to me.

I thought Anna-Maria had a use-case for this.
I just wanted to point out that this patch could potentially
increase the energy consumption for her use-case, nothing more,

Regards,
Pierre

> 
> Thanks,
> 
>          tglx