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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7A3DC2B9F7 for ; Fri, 28 May 2021 14:24:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B1305613C9 for ; Fri, 28 May 2021 14:24:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235543AbhE1O0L (ORCPT ); Fri, 28 May 2021 10:26:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60360 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233298AbhE1O0K (ORCPT ); Fri, 28 May 2021 10:26:10 -0400 Received: from mail-lf1-x135.google.com (mail-lf1-x135.google.com [IPv6:2a00:1450:4864:20::135]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 530ADC061574 for ; Fri, 28 May 2021 07:24:35 -0700 (PDT) Received: by mail-lf1-x135.google.com with SMTP id e17so5622114lfb.2 for ; Fri, 28 May 2021 07:24:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=0qB23gabRSVjg16uX7Swp2PUtcfjaqZT0ss7Q1VTLtc=; b=IvyyHPQK78oRsjX1trLtzkEWbZQcBcxDmBNKDEIV+TWkLXpTAhEGYGhUT825yUWDe3 HOvyK8czIZ8a/ziv8VdJNnsD9f+hyMTaBr5Z+11W2jfphSAUBUxWQl/JWAt3zOXKWK6+ 6WUWRnllmUwqo5uppaUBK2Cq3Rv0mk1NHU+hMS8DvwcBKuUtoI1WQEn+wFV1v1D7FR0h R2FBAsikMQO2RkiEx0k/I7Q6IjnpFTWHC+wDb7pTIoo6GmvpGAtbG/NQcT5d/sPtZGxB iedBqp2shjY21Mr6l5/B2DiYGmsxz8ofmdNn4UGqxsp/a7/6//BIkloKnws+EG6oNOB2 sx1A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=0qB23gabRSVjg16uX7Swp2PUtcfjaqZT0ss7Q1VTLtc=; b=MwBurg2qGnZAc5pa68XfWu4I6+RIz/AMbc11hOkKwOVAVlqFSd2acj3nFFQyCUjC3G ZzWAS12Y4IT4Jlj9LHpUYoIhcnpHVjXIz1bBOUwag+/EHWDb4XRWtOqBwEb7fgfmYMXh yde6ZT539ukOXGpy9eHCRknqIm7GKg2Z8toiCptUj/x+qgBG7EFFyawLFmgpQTmGEsSi N5EfVQNCxcDCAIBBsJfX2ofle0SOPX176YUX2hpTBE0dyUOYnDneKsmPntHlQV2wPuZU 4NuKaKbi3K9hXtDb5wcd4kufjYJG8XetnQMqNSIVmPyC4Kqz/XA/csHCD+00Y1oZslXq OQ6g== X-Gm-Message-State: AOAM5313uRumkkMYPYJkAjD14y/cHJAZCeoG3yBDuZyK1ye8ZMqAhJCW zMcOiKZMsKKdoCwrwRl77fgDUxXt9aomX9307l6P9g== X-Google-Smtp-Source: ABdhPJy0F/Mm6KcZwDdOCTk1XjyjllVwhD7rJDCScs/W95trYbOm2PhE+XQkRRJf8qLMPSwvPnMGq4ehF/H4gBq/Jbk= X-Received: by 2002:ac2:5111:: with SMTP id q17mr6128288lfb.277.1622211873614; Fri, 28 May 2021 07:24:33 -0700 (PDT) MIME-Version: 1.0 References: <20210518125202.78658-1-odin@uged.al> <20210518125202.78658-3-odin@uged.al> In-Reply-To: <20210518125202.78658-3-odin@uged.al> From: Vincent Guittot Date: Fri, 28 May 2021 16:24:22 +0200 Message-ID: Subject: Re: [PATCH 2/3] sched/fair: Correctly insert cfs_rq's to list on unthrottle To: Odin Ugedal Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , "open list:CONTROL GROUP (CGROUP)" , linux-kernel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 18 May 2021 at 14:54, Odin Ugedal wrote: > > This fixes an issue where fairness is decreased since cfs_rq's can > end up not being decayed properly. For two sibling control groups with > the same priority, this can often lead to a load ratio of 99/1 (!!). > > This happen because when a cfs_rq is throttled, all the descendant cfs_rq's > will be removed from the leaf list. When they initial cfs_rq is > unthrottled, it will currently only re add descendant cfs_rq's if they > have one or more entities enqueued. This is not a perfect heuristic. What would be the other condition in addition to the current one :cfs_rq->nr_running >= 1 ? We need to add a cfs_rq in the list if it still contributes to the tg->load_avg and the split of the share. Can't we add a condition for this instead of adding a new field ? > > This fix change this behavior to save what cfs_rq's was removed from the > list, and readds them properly on unthrottle. > > Can often lead to sutiations like this for equally weighted control > groups: > > $ ps u -C stress > USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND > root 10009 88.8 0.0 3676 100 pts/1 R+ 11:04 0:13 stress --cpu 1 > root 10023 3.0 0.0 3676 104 pts/1 R+ 11:04 0:00 stress --cpu 1 > > Fixes: 31bc6aeaab1d ("sched/fair: Optimize update_blocked_averages()") > Signed-off-by: Odin Ugedal > --- > kernel/sched/fair.c | 11 ++++++----- > kernel/sched/sched.h | 1 + > 2 files changed, 7 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index ceda53c2a87a..e7423d658389 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -376,7 +376,8 @@ static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq) > return false; > } > > -static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq) > +/* Returns 1 if cfs_rq was present in the list and removed */ > +static inline bool list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq) > { > if (cfs_rq->on_list) { > struct rq *rq = rq_of(cfs_rq); > @@ -393,7 +394,9 @@ static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq) > > list_del_rcu(&cfs_rq->leaf_cfs_rq_list); > cfs_rq->on_list = 0; > + return 1; > } > + return 0; > } > > static inline void assert_list_leaf_cfs_rq(struct rq *rq) > @@ -4742,9 +4745,7 @@ static int tg_unthrottle_up(struct task_group *tg, void *data) > if (!cfs_rq->throttle_count) { > cfs_rq->throttled_clock_task_time += rq_clock_task(rq) - > cfs_rq->throttled_clock_task; > - > - /* Add cfs_rq with already running entity in the list */ > - if (cfs_rq->nr_running >= 1) > + if (cfs_rq->insert_on_unthrottle) > list_add_leaf_cfs_rq(cfs_rq); > } > > @@ -4759,7 +4760,7 @@ static int tg_throttle_down(struct task_group *tg, void *data) > /* group is entering throttled state, stop time */ > if (!cfs_rq->throttle_count) { > cfs_rq->throttled_clock_task = rq_clock_task(rq); > - list_del_leaf_cfs_rq(cfs_rq); > + cfs_rq->insert_on_unthrottle = list_del_leaf_cfs_rq(cfs_rq); > } > cfs_rq->throttle_count++; > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index a189bec13729..12a707d99ee6 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -602,6 +602,7 @@ struct cfs_rq { > u64 throttled_clock_task_time; > int throttled; > int throttle_count; > + int insert_on_unthrottle; > struct list_head throttled_list; > #endif /* CONFIG_CFS_BANDWIDTH */ > #endif /* CONFIG_FAIR_GROUP_SCHED */ > -- > 2.31.1 >