From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DF56AE77371 for ; Sat, 30 Sep 2023 11:55:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234169AbjI3LqF (ORCPT ); Sat, 30 Sep 2023 07:46:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35382 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230465AbjI3LqE (ORCPT ); Sat, 30 Sep 2023 07:46:04 -0400 Received: from smtpout.efficios.com (smtpout.efficios.com [167.114.26.122]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 41BDBD6 for ; Sat, 30 Sep 2023 04:46:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1696074356; bh=BwM+qiiSjT1rizB6dAsk8vCl4yMw7XPT8jMNJNoi4ZM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=O9TXPcuv1INo2O/LEVGwoMn7GBtYbSLD9JigUWTf/gPPFSAPxzNXXj5nnVm8basaf uRORdbD/5Q75Q3fCrfkzJ+u3C6tS4tNT9wlP45TDKvYIimJYx7TgUG0NNsVcaMbXoY JSDImIPSuIHcseoi98qIyE5XS4FjWvxBs/LJ4UY4YnyLZ4TtD0GrSFSGuxnpLjhLsv KEEbxRjpAj4Rl4+j+UUOcux8+RQEd654mjO9NKni0CNExGZnLOAWovEF6kZBq24hRp MjI5P+ujwAJMV3VcMtFGKBbNb303RvMO0Rfdp8WCHphkIv+26sVyJ7upwgt6lynDPg IVYHvsvU8fLmA== Received: from [IPV6:2606:6d00:100:4000:cacb:9855:de1f:ded2] (unknown [IPv6:2606:6d00:100:4000:cacb:9855:de1f:ded2]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4RyQQX3vp9z1Rh8; Sat, 30 Sep 2023 07:45:56 -0400 (EDT) Message-ID: <0f3cfff3-0df4-3cb7-95cb-ea378517e13b@efficios.com> Date: Sat, 30 Sep 2023 07:45:38 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [RFC PATCH] sched/fair: Bias runqueue selection towards almost idle prev CPU Content-Language: en-US To: Chen Yu Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Ingo Molnar , Valentin Schneider , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Vincent Guittot , Juri Lelli , Swapnil Sapkal , Aaron Lu , Tim Chen , K Prateek Nayak , "Gautham R . Shenoy" , x86@kernel.org References: <20230929183350.239721-1-mathieu.desnoyers@efficios.com> From: Mathieu Desnoyers In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/30/23 03:11, Chen Yu wrote: > Hi Mathieu, > > On 2023-09-29 at 14:33:50 -0400, Mathieu Desnoyers wrote: >> Introduce the WAKEUP_BIAS_PREV_IDLE scheduler feature. It biases >> select_task_rq towards the previous CPU if it was almost idle >> (avg_load <= 0.1%). > > Yes, this is a promising direction IMO. One question is that, > can cfs_rq->avg.load_avg be used for percentage comparison? > If I understand correctly, load_avg reflects that more than > 1 tasks could have been running this runqueue, and the > load_avg is the direct proportion to the load_weight of that > cfs_rq. Besides, LOAD_AVG_MAX seems to not be the max value > that load_avg can reach, it is the sum of > 1024 * (y + y^1 + y^2 ... ) > > For example, > taskset -c 1 nice -n -20 stress -c 1 > cat /sys/kernel/debug/sched/debug | grep 'cfs_rq\[1\]' -A 12 | grep "\.load_avg" > .load_avg : 88763 > .load_avg : 1024 > > 88763 is higher than LOAD_AVG_MAX=47742 I would have expected the load_avg to be limited to LOAD_AVG_MAX somehow, but it appears that it does not happen in practice. That being said, if the cutoff is really at 0.1% or 0.2% of the real max, does it really matter ? > Maybe the util_avg can be used for precentage comparison I suppose? [...] > Or > return cpu_util_without(cpu_rq(cpu), p) * 1000 <= capacity_orig_of(cpu) ? Unfortunately using util_avg does not seem to work based on my testing. Even at utilization thresholds at 0.1%, 1% and 10%. Based on comments in fair.c: * CPU utilization is the sum of running time of runnable tasks plus the * recent utilization of currently non-runnable tasks on that CPU. I think we don't want to include currently non-runnable tasks in the statistics we use, because we are trying to figure out if the cpu is a idle-enough target based on the tasks which are currently running, for the purpose of runqueue selection when waking up a task which is considered at that point in time a non-runnable task on that cpu, and which is about to become runnable again. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com