From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 621BF17BDD for ; Mon, 15 Jan 2024 15:41:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1AA122F4; Mon, 15 Jan 2024 07:42:15 -0800 (PST) Received: from [10.34.100.129] (e126645.nice.arm.com [10.34.100.129]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8A5243F73F; Mon, 15 Jan 2024 07:41:26 -0800 (PST) Message-ID: Date: Mon, 15 Jan 2024 16:41:25 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched/idle: Prevent stopping the tick when there is no cpuidle driver Content-Language: en-US To: Vincent Guittot Cc: Thomas Gleixner , Anna-Maria Behnsen , linux-kernel@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider References: <20231215130501.24542-1-anna-maria@linutronix.de> <87ttnmiif9.fsf@somnus> <06a2561f-557b-4eaa-8f11-75883bbbaef9@arm.com> <87a5pag6q7.fsf@somnus> <87mstaioy6.ffs@tglx> From: Pierre Gondois In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/15/24 14:29, Vincent Guittot wrote: > On Mon, 15 Jan 2024 at 13:40, Pierre Gondois wrote: >> >> 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 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. > > Don't know if it's really a valid use case but can't we have VMs in > such a configuration ? > NOHZ enabled and no cpuidle driver as VM doesn't manage HW anyway ? Yes right, I tried with a kvmtool generated VM and it seemed to be the case: $ grep . /sys/devices/system/cpu/cpuidle/* /sys/devices/system/cpu/cpuidle/available_governors:menu /sys/devices/system/cpu/cpuidle/current_driver:none /sys/devices/system/cpu/cpuidle/current_governor:menu /sys/devices/system/cpu/cpuidle/current_governor_ro:menu > >> >> 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