From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 374D625C704; Tue, 25 Mar 2025 12:37:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742906226; cv=none; b=PJe65L8zvJ1d7W3BUrUvQaTJVMx/EZdxjqCXGU6jvjOp1coURHROteLApqgQO65cXVN8fz9EMKquFfmqgKzvujaiUTUfQDZfk9Q0R+1LWhnu4iwD98+EcZFwJUPMZWqsbFGWqoKGCOUFWiY62T2MetiNGe6QS3fyKwLv1jmMpts= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742906226; c=relaxed/simple; bh=WJwCzn0+W0v2opICXevCIGsJjX02+jDp26ZEywwVoKU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=bWdiOOSAoVFmV2Gsg8LikKMncO8+P/Q7fDetPflIjZoPoGVtgD4L5eG11ZseGlf8MuxgEAQ9aDednLGs9zySfYfo7RK9vN5rIvmPcFwP0VEljnu2AB38ukvxQd9eXKFohc05LPudQXyDGUmJAVCZZmwDVAfOat42vxDeIslvqTU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ELor0Xn0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="ELor0Xn0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DC90FC4CEE4; Tue, 25 Mar 2025 12:37:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1742906226; bh=WJwCzn0+W0v2opICXevCIGsJjX02+jDp26ZEywwVoKU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ELor0Xn08w0Us+xCQUyC4N5OCoDkErfp//BMRhWfVWnnR+GdLNLTF2vnRARcymKfI e8bf7Lf6d7SRbAtFK6KnbzncBVlUJu5ZCgJdyzdFsnckU873Xb8QK2OktZYWtE2UVv ebHXAjVM0iTzgLrTaiXJw2biM5+IDSULH+W9mx54= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Hazem Mohamed Abuelfotoh , Dietmar Eggemann , "Peter Zijlstra (Intel)" , Ingo Molnar , Vincent Guittot , Hagar Hemdan , Linus Torvalds Subject: [PATCH 6.6 72/77] Revert "sched/core: Reduce cost of sched_move_task when config autogroup" Date: Tue, 25 Mar 2025 08:23:07 -0400 Message-ID: <20250325122146.301672233@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250325122144.259256924@linuxfoundation.org> References: <20250325122144.259256924@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dietmar Eggemann commit 76f970ce51c80f625eb6ddbb24e9cb51b977b598 upstream. This reverts commit eff6c8ce8d4d7faef75f66614dd20bb50595d261. Hazem reported a 30% drop in UnixBench spawn test with commit eff6c8ce8d4d ("sched/core: Reduce cost of sched_move_task when config autogroup") on a m6g.xlarge AWS EC2 instance with 4 vCPUs and 16 GiB RAM (aarch64) (single level MC sched domain): https://lkml.kernel.org/r/20250205151026.13061-1-hagarhem@amazon.com There is an early bail from sched_move_task() if p->sched_task_group is equal to p's 'cpu cgroup' (sched_get_task_group()). E.g. both are pointing to taskgroup '/user.slice/user-1000.slice/session-1.scope' (Ubuntu '22.04.5 LTS'). So in: do_exit() sched_autogroup_exit_task() sched_move_task() if sched_get_task_group(p) == p->sched_task_group return /* p is enqueued */ dequeue_task() \ sched_change_group() | task_change_group_fair() | detach_task_cfs_rq() | (1) set_task_rq() | attach_task_cfs_rq() | enqueue_task() / (1) isn't called for p anymore. Turns out that the regression is related to sgs->group_util in group_is_overloaded() and group_has_capacity(). If (1) isn't called for all the 'spawn' tasks then sgs->group_util is ~900 and sgs->group_capacity = 1024 (single CPU sched domain) and this leads to group_is_overloaded() returning true (2) and group_has_capacity() false (3) much more often compared to the case when (1) is called. I.e. there are much more cases of 'group_is_overloaded' and 'group_fully_busy' in WF_FORK wakeup sched_balance_find_dst_cpu() which then returns much more often a CPU != smp_processor_id() (5). This isn't good for these extremely short running tasks (FORK + EXIT) and also involves calling sched_balance_find_dst_group_cpu() unnecessary (single CPU sched domain). Instead if (1) is called for 'p->flags & PF_EXITING' then the path (4),(6) is taken much more often. select_task_rq_fair(..., wake_flags = WF_FORK) cpu = smp_processor_id() new_cpu = sched_balance_find_dst_cpu(..., cpu, ...) group = sched_balance_find_dst_group(..., cpu) do { update_sg_wakeup_stats() sgs->group_type = group_classify() if group_is_overloaded() (2) return group_overloaded if !group_has_capacity() (3) return group_fully_busy return group_has_spare (4) } while group if local_sgs.group_type > idlest_sgs.group_type return idlest (5) case group_has_spare: if local_sgs.idle_cpus >= idlest_sgs.idle_cpus return NULL (6) Unixbench Tests './Run -c 4 spawn' on: (a) VM AWS instance (m7gd.16xlarge) with v6.13 ('maxcpus=4 nr_cpus=4') and Ubuntu 22.04.5 LTS (aarch64). Shell & test run in '/user.slice/user-1000.slice/session-1.scope'. w/o patch w/ patch 21005 27120 (b) i7-13700K with tip/sched/core ('nosmt maxcpus=8 nr_cpus=8') and Ubuntu 22.04.5 LTS (x86_64). Shell & test run in '/A'. w/o patch w/ patch 67675 88806 CONFIG_SCHED_AUTOGROUP=y & /sys/proc/kernel/sched_autogroup_enabled equal 0 or 1. Reported-by: Hazem Mohamed Abuelfotoh Signed-off-by: Dietmar Eggemann Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Vincent Guittot Tested-by: Hagar Hemdan Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250314151345.275739-1-dietmar.eggemann@arm.com [Hagar: clean revert of eff6c8ce8dd7 to make it work on 6.6] Signed-off-by: Hagar Hemdan Signed-off-by: Greg Kroah-Hartman --- kernel/sched/core.c | 22 +++------------------- 1 file changed, 3 insertions(+), 19 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -10494,7 +10494,7 @@ void sched_release_group(struct task_gro spin_unlock_irqrestore(&task_group_lock, flags); } -static struct task_group *sched_get_task_group(struct task_struct *tsk) +static void sched_change_group(struct task_struct *tsk) { struct task_group *tg; @@ -10506,13 +10506,7 @@ static struct task_group *sched_get_task tg = container_of(task_css_check(tsk, cpu_cgrp_id, true), struct task_group, css); tg = autogroup_task_group(tsk, tg); - - return tg; -} - -static void sched_change_group(struct task_struct *tsk, struct task_group *group) -{ - tsk->sched_task_group = group; + tsk->sched_task_group = tg; #ifdef CONFIG_FAIR_GROUP_SCHED if (tsk->sched_class->task_change_group) @@ -10533,19 +10527,10 @@ void sched_move_task(struct task_struct { int queued, running, queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK; - struct task_group *group; struct rq_flags rf; struct rq *rq; rq = task_rq_lock(tsk, &rf); - /* - * Esp. with SCHED_AUTOGROUP enabled it is possible to get superfluous - * group changes. - */ - group = sched_get_task_group(tsk); - if (group == tsk->sched_task_group) - goto unlock; - update_rq_clock(rq); running = task_current(rq, tsk); @@ -10556,7 +10541,7 @@ void sched_move_task(struct task_struct if (running) put_prev_task(rq, tsk); - sched_change_group(tsk, group); + sched_change_group(tsk); if (queued) enqueue_task(rq, tsk, queue_flags); @@ -10570,7 +10555,6 @@ void sched_move_task(struct task_struct resched_curr(rq); } -unlock: task_rq_unlock(rq, tsk, &rf); }