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 C4C5CC433EF for ; Mon, 31 Jan 2022 11:32:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233490AbiAaLcQ (ORCPT ); Mon, 31 Jan 2022 06:32:16 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:55130 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1377002AbiAaLWU (ORCPT ); Mon, 31 Jan 2022 06:22:20 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 5972A61298; Mon, 31 Jan 2022 11:22:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 35676C340E8; Mon, 31 Jan 2022 11:22:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1643628139; bh=tcdbW/8UqgiCGn1wuJRWV1j3SX/4Fj4DznIlan+YDvo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ITemSXb4Mw+AlxiC/pViOyB8Cqk/JjeROoQDoNbJ2P5fI1Xifg6qlFK1fzirTnqak 6IDLqq1KPyptEHAjLFVBTCOSiwJNRolGpfmBrQkgvJfDJ9wikwu5tj/Ll9cI70YRFo VSXNiy/Rs4WsfdJWvdUfnT0oNu0UfCU0R8aoR7KE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Rick Yiu , Vincent Guittot , "Peter Zijlstra (Intel)" , Dietmar Eggemann , Sachin Sant , Sasha Levin Subject: [PATCH 5.16 130/200] sched/pelt: Relax the sync of util_sum with util_avg Date: Mon, 31 Jan 2022 11:56:33 +0100 Message-Id: <20220131105237.926644981@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220131105233.561926043@linuxfoundation.org> References: <20220131105233.561926043@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Vincent Guittot [ Upstream commit 98b0d890220d45418cfbc5157b3382e6da5a12ab ] Rick reported performance regressions in bugzilla because of cpu frequency being lower than before: https://bugzilla.kernel.org/show_bug.cgi?id=215045 He bisected the problem to: commit 1c35b07e6d39 ("sched/fair: Ensure _sum and _avg values stay consistent") This commit forces util_sum to be synced with the new util_avg after removing the contribution of a task and before the next periodic sync. By doing so util_sum is rounded to its lower bound and might lost up to LOAD_AVG_MAX-1 of accumulated contribution which has not yet been reflected in util_avg. Instead of always setting util_sum to the low bound of util_avg, which can significantly lower the utilization of root cfs_rq after propagating the change down into the hierarchy, we revert the change of util_sum and propagate the difference. In addition, we also check that cfs's util_sum always stays above the lower bound for a given util_avg as it has been observed that sched_entity's util_sum is sometimes above cfs one. Fixes: 1c35b07e6d39 ("sched/fair: Ensure _sum and _avg values stay consistent") Reported-by: Rick Yiu Signed-off-by: Vincent Guittot Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Dietmar Eggemann Tested-by: Sachin Sant Link: https://lkml.kernel.org/r/20220111134659.24961-2-vincent.guittot@linaro.org Signed-off-by: Sasha Levin --- kernel/sched/fair.c | 16 +++++++++++++--- kernel/sched/pelt.h | 4 +++- 2 files changed, 16 insertions(+), 4 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index f2cf047b25e56..069e01772d922 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3382,7 +3382,6 @@ void set_task_rq_fair(struct sched_entity *se, se->avg.last_update_time = n_last_update_time; } - /* * When on migration a sched_entity joins/leaves the PELT hierarchy, we need to * propagate its contribution. The key to this propagation is the invariant @@ -3450,7 +3449,6 @@ void set_task_rq_fair(struct sched_entity *se, * XXX: only do this for the part of runnable > running ? * */ - static inline void update_tg_cfs_util(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq *gcfs_rq) { @@ -3682,7 +3680,19 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) r = removed_util; sub_positive(&sa->util_avg, r); - sa->util_sum = sa->util_avg * divider; + sub_positive(&sa->util_sum, r * divider); + /* + * Because of rounding, se->util_sum might ends up being +1 more than + * cfs->util_sum. Although this is not a problem by itself, detaching + * a lot of tasks with the rounding problem between 2 updates of + * util_avg (~1ms) can make cfs->util_sum becoming null whereas + * cfs_util_avg is not. + * Check that util_sum is still above its lower bound for the new + * util_avg. Given that period_contrib might have moved since the last + * sync, we are only sure that util_sum must be above or equal to + * util_avg * minimum possible divider + */ + sa->util_sum = max_t(u32, sa->util_sum, sa->util_avg * PELT_MIN_DIVIDER); r = removed_runnable; sub_positive(&sa->runnable_avg, r); diff --git a/kernel/sched/pelt.h b/kernel/sched/pelt.h index e06071bf3472c..c336f5f481bca 100644 --- a/kernel/sched/pelt.h +++ b/kernel/sched/pelt.h @@ -37,9 +37,11 @@ update_irq_load_avg(struct rq *rq, u64 running) } #endif +#define PELT_MIN_DIVIDER (LOAD_AVG_MAX - 1024) + static inline u32 get_pelt_divider(struct sched_avg *avg) { - return LOAD_AVG_MAX - 1024 + avg->period_contrib; + return PELT_MIN_DIVIDER + avg->period_contrib; } static inline void cfs_se_util_change(struct sched_avg *avg) -- 2.34.1