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 BC90712BEBE; Fri, 19 Apr 2024 13:42:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713534144; cv=none; b=eng2nG/D6iD+39DNu9lGmZjYhvVN34eq+rJhjsJXIHuMhUIz/oNZapnpx93q3BGzSS5dNK7abGrxe7rpoizK5e8/68Sa8HA+lKgjdrE/+/1s4UnrySLcP7LdZfy6afRABXvQvOAxXpJpA8OF9YqaJy7hs8m/NySCEd5X6RokLfw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713534144; c=relaxed/simple; bh=2Th4AlJNiK8G7lYUCJU5ZRC6UwKwfk2DPXWCgGmkaZI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=a74iCjzKaglIZvskSIfOUNkF8XGDJmgMKuqf86pPYCDInm8v0sNrzFmHCe1wfiCExs6Usrsyt7FAcMxkOm452ZvCj0Rl8C6S0xBf3kmNOezNN5rwAtSzjdY+BpUlEYmEd+WA/2bZ6s8eQw3Z4E3gGhy0GLn14Om3eClbRroMlGw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 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 6AAE6339; Fri, 19 Apr 2024 06:42:50 -0700 (PDT) Received: from [10.1.30.55] (e133047.arm.com [10.1.30.55]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D05DF3F64C; Fri, 19 Apr 2024 06:42:18 -0700 (PDT) Message-ID: Date: Fri, 19 Apr 2024 14:42:16 +0100 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 2/2] cpufreq/schedutil: Remove iowait boost To: Qais Yousef , "Rafael J. Wysocki" Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, juri.lelli@redhat.com, mingo@redhat.com, dietmar.eggemann@arm.com, vschneid@redhat.com, vincent.guittot@linaro.org, Johannes.Thumshirn@wdc.com, adrian.hunter@intel.com, ulf.hansson@linaro.org, andres@anarazel.de, asml.silence@gmail.com, linux-pm@vger.kernel.org, linux-block@vger.kernel.org, io-uring@vger.kernel.org References: <20240304201625.100619-1-christian.loehle@arm.com> <20240304201625.100619-3-christian.loehle@arm.com> <5060c335-e90a-430f-bca5-c0ee46a49249@arm.com> <20240325023726.itkhlg66uo5kbljx@airbuntu> Content-Language: en-US From: Christian Loehle In-Reply-To: <20240325023726.itkhlg66uo5kbljx@airbuntu> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 25/03/2024 02:37, Qais Yousef wrote: > On 03/18/24 18:08, Rafael J. Wysocki wrote: >> On Mon, Mar 18, 2024 at 5:40 PM Christian Loehle >> wrote: >>> >>> On 18/03/2024 14:07, Rafael J. Wysocki wrote: >>>> On Mon, Mar 4, 2024 at 9:17 PM Christian Loehle >>>> wrote: >>>>> >>>>> The previous commit provides a new cpu_util_cfs_boost_io interface for >>>>> schedutil which uses the io boosted utilization of the per-task >>>>> tracking strategy. Schedutil iowait boosting is therefore no longer >>>>> necessary so remove it. >>>> >>>> I'm wondering about the cases when schedutil is used without EAS. >>>> >>>> Are they still going to be handled as before after this change? >>> >>> Well they should still get boosted (under the new conditions) and according >>> to my tests that does work. >> >> OK >> >>> Anything in particular you're worried about? >> >> It is not particularly clear to me how exactly the boost is taken into >> account without EAS. >> >>> So in terms of throughput I see similar results with EAS and CAS+sugov. >>> I'm happy including numbers in the cover letter for future versions, too. >>> So far my intuition was that nobody would care enough to include them >>> (as long as it generally still works). >> >> Well, IMV clear understanding of the changes is more important. > > I think the major thing we need to be careful about is the behavior when the > task is sleeping. I think the boosting will be removed when the task is > dequeued and I can bet there will be systems out there where the BLOCK softirq > being boosted when the task is sleeping will matter. Currently I see this mainly protected by the sugov rate_limit_us. With the enqueue's being the dominating cpufreq updates it's not really an issue, the boost is expected to survive the sleep duration, during which it wouldn't be active. I did experiment with some sort of 'stickiness' of the boost to the rq, but it is somewhat of a pain to deal with if we want to remove it once enqueued on a different rq. A sugov 1ms timer is much simpler of course. Currently it's not necessary IMO, but for the sake of being future-proof in terms of more frequent freq updates I might include it in v2. > > FWIW I do have an implementation for per-task iowait boost where I went a step > further and converted intel_pstate too and like Christian didn't notice > a regression. But I am not sure (rather don't think) I triggered this use case. > I can't tell when the systems truly have per-cpu cpufreq control or just appear > so and they are actually shared but not visible at linux level. Please do share your intel_pstate proposal! Kind Regards, Christian