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 7A7B419D8B3; Tue, 1 Oct 2024 09:57:10 +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=1727776632; cv=none; b=ngPc1HHrgYMNryDbbJIloEDXlC/Rj39aJfmC1mgWA0YSyXB0FUMVWFK6jOrOnsgrX+sdcs3XWdUIHnkzQoRSedF2jWMb6y3zrhoRxo4971pTrvlOZTG0Ow3+mwL/x+1bSqhKrvbXRxIdMb/Vbk5Gfd/NxmQk6vgsaefGRJbjA4I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727776632; c=relaxed/simple; bh=H0q9iztMRd0pzuiH5IupS+REpCUjAfJeJx6mUfo/qhE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=pmBwrwCB9G/fqD8rOCy2GQM0PVnchdu4iD+1JjLx/ScQ73zvVCCo81+s6Bwy2O8T+93BkNDAavc3cjfU+mYkWQE+V0aWm6B1yjNVV/wld72gwP9wCntyp5ahpknSYCMo5VOa0GRDkz/NHsu2nBYc8Bz9T3WGna2ZfCzoyzmiEuo= 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 1285F339; Tue, 1 Oct 2024 02:57:39 -0700 (PDT) Received: from [10.1.28.63] (e127648.arm.com [10.1.28.63]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 78FFB3F58B; Tue, 1 Oct 2024 02:57:05 -0700 (PDT) Message-ID: Date: Tue, 1 Oct 2024 10:57:03 +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 6/8] cpufreq: intel_pstate: Remove iowait boost To: srinivas pandruvada , "Rafael J. Wysocki" Cc: linux-pm@vger.kernel.org, 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, bvanassche@acm.org, andres@anarazel.de, asml.silence@gmail.com, linux-block@vger.kernel.org, io-uring@vger.kernel.org, qyousef@layalina.io, dsmythies@telus.net, axboe@kernel.dk References: <20240905092645.2885200-1-christian.loehle@arm.com> <20240905092645.2885200-7-christian.loehle@arm.com> <0a0186cad5a9254027d0ac6a7f39e39f5473665c.camel@linux.intel.com> Content-Language: en-US From: Christian Loehle In-Reply-To: <0a0186cad5a9254027d0ac6a7f39e39f5473665c.camel@linux.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/30/24 21:35, srinivas pandruvada wrote: > On Mon, 2024-09-30 at 20:03 +0200, Rafael J. Wysocki wrote: >> +Srinivas who can say more about the reasons why iowait boosting >> makes >> a difference for intel_pstate than I do. >> Hi Srinivas, > It makes difference on Xeons and also GFX performance. AFAIU the GFX performance with iowait boost is a regression though, because it cuts into the system power budget (CPU+GPU), especially on desktop and mobile chips (but also some servers), no? https://lore.kernel.org/lkml/20180730220029.81983-1-srinivas.pandruvada@linux.intel.com/ https://lore.kernel.org/lkml/e7388bf4-deb1-34b6-97d7-89ced8e78ef1@intel.com/ Or is there a reported case where iowait boosting helps graphics workloads? > The actual gains will be model specific as it will be dependent on > hardware algorithms and EPP. > > It was introduced to solve regression in Skylake xeons. But even in the > recent servers there are gains. > Refer to > https://lkml.iu.edu/hypermail/linux/kernel/1806.0/03574.html Did you look into PELT utilization values at that time? I see why intel_pstate might be worse off than schedutil wrt removing iowait boosting and do see two remedies essentially: 1. Boost after all sleeps (less aggressively), although I'm not a huge fan of this. 2. If the gap between util_est and HWP-determined frequency is too large then apply some boost. A sort of fallback on a schedutil strategy. That would of course require util_est to be significantly large in those scenarios. I might try to propose something for 2, although as you can probably guess, playing with HWP is somewhat uncharted waters for me. Since intel_pstate will actually boost into unsustainable P-states, there should be workloads that regress with iowait boosting. I'll go looking for those.