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 21238EB64DA for ; Thu, 20 Jul 2023 15:04:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232411AbjGTPEf (ORCPT ); Thu, 20 Jul 2023 11:04:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46616 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232139AbjGTPEd (ORCPT ); Thu, 20 Jul 2023 11:04:33 -0400 Received: from mail-ed1-x529.google.com (mail-ed1-x529.google.com [IPv6:2a00:1450:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 45577BB for ; Thu, 20 Jul 2023 08:04:31 -0700 (PDT) Received: by mail-ed1-x529.google.com with SMTP id 4fb4d7f45d1cf-51d95aed33aso1208716a12.3 for ; Thu, 20 Jul 2023 08:04:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1689865470; x=1690470270; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=7aSG/EqU9I5oy5fQXPoCvjc38F4/1Ha3I7wLiLMebnc=; b=LXRHONLbIoaLxmq89NXaIJ4qaJYib7ePx6++u0uBdbGJMLkSeoqleivsbRF7ubTTVW PvSD/HsKMM6LLAKUb+9xt/DXPfvo1J3XRWFbNXPIPAz7ea1NqIG6FQP9TyPtFWfZe5IX FugLgbq0sc3jNxC0MH/RN70WkB9kJKD3yC3cMJGPAHSYeIR9yI4FF3AGo+jogzdCPf1G WeMy9C2368W6iPUiDmb3SL3j7zcS+jU6rtAQv0T8EfRjzOMvspQhu0l9E1lhfSPJE7O/ KmKBKx3nCYLWeWrrU2FmqQwqI6jHk2ENRXd7AXYDhjzgajsiw+6Mb2GWFuPw5OBmjLnM vhqA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1689865470; x=1690470270; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=7aSG/EqU9I5oy5fQXPoCvjc38F4/1Ha3I7wLiLMebnc=; b=WU2soN/bsDHGv9XczUn4uNRPdfhhRGFOxuGoSMwLgL8cfU959OEq7Vz8H2D/RAWT/D bQZ1FzCxcZmKTRHGxDNzZ9YvDdMPKbaMT0kiJ7HIaDnz/Yt8OtzNkoorKQgRNeutFeal DwnBQYVHjm0+eFcD+IYeyR8U40D6wrYTYsV7qf2PpWSuETE3M8+uG/UxVgqyaznvanz8 IwzVDAQ/9+tDcWIL6tflyiH9Fnx1AMVVu8LKPRqei76O4MZmwnxwBswovTRPUN2t2J3c AhsBKpjgFt8sr29MRgML2HGq+N8TS+l6njaSXrENbORGCW8LbMhHyYWhL0+KdQhn7PcQ yc/A== X-Gm-Message-State: ABy/qLaNfUx2t0vZ4s5ApYPTtVajDM7Eht7aiFuFhNGeenJNiowcStfp zMce7Gd392y/38W5Uxo5u4Od3dEQo06bcKq/TmG0yQ== X-Google-Smtp-Source: APBJJlH9lmghh4l44WkdwYIQOatd/BtNQnH7v3/47BBuIrYB8vIuRx0N0JLtAcVMJPw0tJYG2wCsfTPPsWyjjCtpyxM= X-Received: by 2002:aa7:d145:0:b0:51b:e4c7:410f with SMTP id r5-20020aa7d145000000b0051be4c7410fmr4710171edo.6.1689865469711; Thu, 20 Jul 2023 08:04:29 -0700 (PDT) MIME-Version: 1.0 References: <20230718134120.81199-1-aaron.lu@intel.com> <20230718134120.81199-4-aaron.lu@intel.com> <20230719051826.GB84059@ziqianlu-dell> <20230719080105.GA90441@ziqianlu-dell> <20230719132914.GA91858@ziqianlu-dell> <20230720144233.GA185317@ziqianlu-dell> In-Reply-To: <20230720144233.GA185317@ziqianlu-dell> From: Vincent Guittot Date: Thu, 20 Jul 2023 17:04:18 +0200 Message-ID: Subject: Re: [RFC PATCH 3/4] sched/fair: delay update_tg_load_avg() for cfs_rq's removed load To: Aaron Lu Cc: Peter Zijlstra , Ingo Molnar , Juri Lelli , Daniel Jordan , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , Tim Chen , Nitin Tekchandani , Yu Chen , Waiman Long , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 20 Jul 2023 at 16:42, Aaron Lu wrote: > > On Thu, Jul 20, 2023 at 03:10:30PM +0200, Vincent Guittot wrote: > > On Wed, 19 Jul 2023 at 15:29, Aaron Lu wrote: > > > > > > On Wed, Jul 19, 2023 at 11:47:06AM +0200, Vincent Guittot wrote: > > > > On Wed, 19 Jul 2023 at 10:01, Aaron Lu wrote: > > > > > > > > > > On Wed, Jul 19, 2023 at 01:18:26PM +0800, Aaron Lu wrote: > > > > > > Alternatively, I can remove some callsites of update_tg_load_avg() like > > > > > > you suggested below and only call update_tg_load_avg() when cfs_rq is > > > > > > decayed(really just decayed, not when it detected it has removed load > > > > > > pending or load propagated from its children). This way it would give us > > > > > > similar result as above(roughly once per ms). > > > > > > > > > > Something like this: (I think this is better since it removed those > > > > > unnecessary calls to update_tg_load_avg(), although it is inline but > > > > > still) > > > > > > > > > > > > > > > From bc749aaefa6bed36aa946921a4006b3dddb69b77 Mon Sep 17 00:00:00 2001 > > > > > From: Aaron Lu > > > > > Date: Wed, 19 Jul 2023 13:54:48 +0800 > > > > > Subject: [PATCH] sched/fair: only update_tg_load_avg() when cfs_rq decayed > > > > > > > > > > --- > > > > > kernel/sched/fair.c | 22 +++++++--------------- > > > > > 1 file changed, 7 insertions(+), 15 deletions(-) > > > > > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > > > index a80a73909dc2..7d5b7352b8b5 100644 > > > > > --- a/kernel/sched/fair.c > > > > > +++ b/kernel/sched/fair.c > > > > > @@ -3913,16 +3913,16 @@ static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum > > > > > } > > > > > > > > > > /* Update task and its cfs_rq load average */ > > > > > -static inline int propagate_entity_load_avg(struct sched_entity *se) > > > > > +static inline void propagate_entity_load_avg(struct sched_entity *se) > > > > > { > > > > > struct cfs_rq *cfs_rq, *gcfs_rq; > > > > > > > > > > if (entity_is_task(se)) > > > > > - return 0; > > > > > + return; > > > > > > > > > > gcfs_rq = group_cfs_rq(se); > > > > > if (!gcfs_rq->propagate) > > > > > - return 0; > > > > > + return; > > > > > > > > > > gcfs_rq->propagate = 0; > > > > > > > > > > @@ -3936,8 +3936,6 @@ static inline int propagate_entity_load_avg(struct sched_entity *se) > > > > > > > > > > trace_pelt_cfs_tp(cfs_rq); > > > > > trace_pelt_se_tp(se); > > > > > - > > > > > - return 1; > > > > > } > > > > > > > > > > /* > > > > > @@ -3974,9 +3972,8 @@ static inline bool skip_blocked_update(struct sched_entity *se) > > > > > > > > > > static inline void update_tg_load_avg(struct cfs_rq *cfs_rq) {} > > > > > > > > > > -static inline int propagate_entity_load_avg(struct sched_entity *se) > > > > > +static inline void propagate_entity_load_avg(struct sched_entity *se) > > > > > { > > > > > - return 0; > > > > > } > > > > > > > > > > static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum) {} > > > > > @@ -4086,7 +4083,7 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) > > > > > { > > > > > unsigned long removed_load = 0, removed_util = 0, removed_runnable = 0; > > > > > struct sched_avg *sa = &cfs_rq->avg; > > > > > - int decayed = 0; > > > > > + int decayed; > > > > > > > > > > if (cfs_rq->removed.nr) { > > > > > unsigned long r; > > > > > @@ -4134,11 +4131,9 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) > > > > > */ > > > > > add_tg_cfs_propagate(cfs_rq, > > > > > -(long)(removed_runnable * divider) >> SCHED_CAPACITY_SHIFT); > > > > > - > > > > > - decayed = 1; > > > > > } > > > > > > > > > > - decayed |= __update_load_avg_cfs_rq(now, cfs_rq); > > > > > + decayed = __update_load_avg_cfs_rq(now, cfs_rq); > > > > > u64_u32_store_copy(sa->last_update_time, > > > > > cfs_rq->last_update_time_copy, > > > > > sa->last_update_time); > > > > > @@ -4252,7 +4247,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s > > > > > __update_load_avg_se(now, cfs_rq, se); > > > > > > > > > > decayed = update_cfs_rq_load_avg(now, cfs_rq); > > > > > - decayed |= propagate_entity_load_avg(se); > > > > > + propagate_entity_load_avg(se); > > > > > > > > but then you also skip the call to cfs_rq_util_change() > > > > > > Ah right, I missed that, thanks for catching this. > > > > > > Updated: > > > > > > From 09a649f8111cfca656b7b735da975ef607b00956 Mon Sep 17 00:00:00 2001 > > > From: Aaron Lu > > > Date: Wed, 19 Jul 2023 13:54:48 +0800 > > > Subject: [PATCH] sched/fair: only update_tg_load_avg() when cfs_rq decayed > > > > > > --- > > > kernel/sched/fair.c | 17 ++++++----------- > > > 1 file changed, 6 insertions(+), 11 deletions(-) > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > index a80a73909dc2..8d4b9e0a19b6 100644 > > > --- a/kernel/sched/fair.c > > > +++ b/kernel/sched/fair.c > > > @@ -4086,7 +4086,7 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) > > > { > > > unsigned long removed_load = 0, removed_util = 0, removed_runnable = 0; > > > struct sched_avg *sa = &cfs_rq->avg; > > > - int decayed = 0; > > > + int decayed; > > > > > > if (cfs_rq->removed.nr) { > > > unsigned long r; > > > @@ -4134,11 +4134,9 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) > > > */ > > > add_tg_cfs_propagate(cfs_rq, > > > -(long)(removed_runnable * divider) >> SCHED_CAPACITY_SHIFT); > > > - > > > - decayed = 1; > > > > We need this to propagate the change in other place like cpufreq > > Ah, I just made the same mistake again, sorry. > > So there are three cases for a cfs_rq: load decayed, load removed and > load propagated. For all three cases, cfs_rq_util_change() needs to be > called and only for decayed, update_tg_load_avg() needs to be called. > > I'll update the patch accordingly. > > > > } > > > > > > - decayed |= __update_load_avg_cfs_rq(now, cfs_rq); > > > + decayed = __update_load_avg_cfs_rq(now, cfs_rq); > > > u64_u32_store_copy(sa->last_update_time, > > > cfs_rq->last_update_time_copy, > > > sa->last_update_time); > > > @@ -4242,7 +4240,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s > > > static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) > > > { > > > u64 now = cfs_rq_clock_pelt(cfs_rq); > > > - int decayed; > > > + int decayed, propagated; > > > > > > /* > > > * Track task load average for carrying it to new CPU after migrated, and > > > @@ -4252,7 +4250,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s > > > __update_load_avg_se(now, cfs_rq, se); > > > > > > decayed = update_cfs_rq_load_avg(now, cfs_rq); > > > - decayed |= propagate_entity_load_avg(se); > > > + propagated = propagate_entity_load_avg(se); > > > > > > if (!se->avg.last_update_time && (flags & DO_ATTACH)) { > > > > > > @@ -4264,19 +4262,16 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s > > > * IOW we're enqueueing a task on a new CPU. > > > */ > > > attach_entity_load_avg(cfs_rq, se); > > > - update_tg_load_avg(cfs_rq); > > > - > > > } else if (flags & DO_DETACH) { > > > /* > > > * DO_DETACH means we're here from dequeue_entity() > > > * and we are migrating task out of the CPU. > > > */ > > > detach_entity_load_avg(cfs_rq, se); > > > - update_tg_load_avg(cfs_rq); > > > - } else if (decayed) { > > > + } else if (decayed || propagated) { > > > cfs_rq_util_change(cfs_rq, 0); > > > > > > - if (flags & UPDATE_TG) > > > + if (decayed && (flags & UPDATE_TG)) > > > > It would be simpler and more readable to clear UPDATE_TG or not set it > > from the beginning > > Do you mean something like this? > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 8d4b9e0a19b6..084d63371355 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4249,7 +4249,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s > if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD)) > __update_load_avg_se(now, cfs_rq, se); > > - decayed = update_cfs_rq_load_avg(now, cfs_rq); > + decayed = update_cfs_rq_load_avg(now, cfs_rq) && (flags & UPDATE_TG); > propagated = propagate_entity_load_avg(se); > > if (!se->avg.last_update_time && (flags & DO_ATTACH)) { > @@ -4271,7 +4271,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s > } else if (decayed || propagated) { > cfs_rq_util_change(cfs_rq, 0); > > - if (decayed && (flags & UPDATE_TG)) > + if (decayed) > update_tg_load_avg(cfs_rq); > } something like below: --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4252,6 +4252,8 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s __update_load_avg_se(now, cfs_rq, se); decayed = update_cfs_rq_load_avg(now, cfs_rq); + if (!decayed) + flags &= ~UPDATE_TG; decayed |= propagate_entity_load_avg(se); if (!se->avg.last_update_time && (flags & DO_ATTACH)) { > } > > > IIUC, you rely on the fact that a decay happens every 1024 us of the > > cfs_rq_clock_pelt() which is scaled by frequency and cpu compute > > capacity. So you can end up with a cfs_rq_clock_pelt() that is far > > slower than real clock and the 1ms can easily be extended to dozens of > > ms > > Thanks for the info. I'm not familiar with this clock scale part and will > need to take a closer look. > > As you know, the intent is to make the unbound update to tg->load_avg > become bound for those wakeup migration heavy workloads and the way this > change does to achieve it is to remove the update to tg->load_avg on > attach and detach path, just leave the update on load decay path. And if > the current implementation makes load decay longer than 1024us, that > shouldn't be a problem for this change. I don't see an immediate problem > if update to tg->load_avg happens less often than once per ms but please > let me know if I missed something, thanks. > > > > > > update_tg_load_avg(cfs_rq); > > > } > > > } > > > -- > > > 2.41.0 > > > > > > > > > > > > > > > > if (!se->avg.last_update_time && (flags & DO_ATTACH)) { > > > > > > > > > > @@ -4264,15 +4259,12 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s > > > > > * IOW we're enqueueing a task on a new CPU. > > > > > */ > > > > > attach_entity_load_avg(cfs_rq, se); > > > > > - update_tg_load_avg(cfs_rq); > > > > > - > > > > > } else if (flags & DO_DETACH) { > > > > > /* > > > > > * DO_DETACH means we're here from dequeue_entity() > > > > > * and we are migrating task out of the CPU. > > > > > */ > > > > > detach_entity_load_avg(cfs_rq, se); > > > > > - update_tg_load_avg(cfs_rq); > > > > > } else if (decayed) { > > > > > cfs_rq_util_change(cfs_rq, 0); > > > > > > > > > > -- > > > > > 2.41.0 > > > > >