From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta1.migadu.com (out-177.mta1.migadu.com [95.215.58.177]) (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 2A55A3254A8 for ; Wed, 24 Jun 2026 05:52:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782280337; cv=none; b=ozK7h7dpE+bVr/yrKJTz5Q3csXRj3J71WoL+n6snMxVq6HeGG2t0HontWO1/fLMEySWiQipqsf20EEMMFq44JTk+nNM1w95FYblibwR5X/1pfihjH3innISgGdxykRZ+NDtMAIigYZyv59PlmyrFK60I/aOxWHeM8bG9ZxRUIhY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782280337; c=relaxed/simple; bh=lNutLdgBVcfzaSe0zfB/rgX3VF9ibBXkW6a8qpgoRD0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JblwVYkclOU8WYiQTxzbSZCvXfkh5ao8J7j5rwFdf46OByZYvBQsM7OKLcEudKl5N7qnpKIEDCy+dl+vf7vMwbilNmMu0Z+MYoANtBGmSdtCV01oKWTVu13kWxRRi9KSzlSabsFxCVDUuElFxU2as/W69yWuGTKvhjpceqpIE2E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=PJvOU0yi; arc=none smtp.client-ip=95.215.58.177 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="PJvOU0yi" Message-ID: <2c59b7b7-a3c0-4799-8c39-2288299b117e@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782280332; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=RsiEnXmUmSVLGgTWzqORpnaRJ3h8lAWFGgmjylcqD+Q=; b=PJvOU0yiGiDiKEW2Cb5tXVqblMIshjWRqG6uo7ZDMW152GopB276SmE7xkoKyNWI4DywHc b6yPTTd6geCzZqYA4BUq8qaXuq7K4NLe69u8o2SBvIt/JVE8YtJA4zKgpBjrfPcrcdhHDr vZ88B4C/16mQFWAd+iLuwxOdNBAqETI= Date: Wed, 24 Jun 2026 13:51:46 +0800 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v2 1/2] cgroup/cpuset: Avoid unnecessary cpus & mems update in cpuset_hotplug_update_tasks() To: Waiman Long , Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Jonathan Corbet , Shuah Khan Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20260623230413.1984188-1-longman@redhat.com> <20260623230413.1984188-2-longman@redhat.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Ridong Chen In-Reply-To: <20260623230413.1984188-2-longman@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 6/24/2026 7:04 AM, Waiman Long wrote: > As reported by sashiko [1], cpuset_hotplug_update_tasks() may perform > unnecessary task iteration and updating of tasks' CPU and node masks > when mems_allowed and/or cpus_allowed are not set in cpuset v2. It is > due to the fact that the temporary new_cpus and new_mems masks do not > inherit parent's effective_cpus/mems when they are empty which is the > expected behavior for cpuset v2 since commit 4ec22e9c5a90 ("cpuset: > Enable cpuset controller in default hierarchy"). > > Fix that and avoid unnecessay work by enhancing > compute_effective_cpumask() to add the empty cpumask check > and inheriting the parent's versions if empty when in v2. A new > compute_effective_nodemask() helper is also added to perform similar > function for new effective_mems. > > Add new test_cpuset_prs.sh test cases to confirm that effective_cpus > will inherit the parent's version if cpuset.cpus is empty. > > [1] https://sashiko.dev/#/patchset/20260621032816.1806773-1-longman%40redhat.com > > Suggested-by: Ridong Chen > Fixes: 4ec22e9c5a90 ("cpuset: Enable cpuset controller in default hierarchy") > Signed-off-by: Waiman Long > --- > kernel/cgroup/cpuset.c | 45 +++++++++++-------- > .../selftests/cgroup/test_cpuset_prs.sh | 11 ++++- > 2 files changed, 35 insertions(+), 21 deletions(-) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index aff86acea701..044ddbf66f8e 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -1094,12 +1094,35 @@ void cpuset_update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus) > * @cs: the cpuset the need to recompute the new effective_cpus mask > * @parent: the parent cpuset > * > + * For v2, the parent's effective_cpus is inherited if cpumask empty. > * The result is valid only if the given cpuset isn't a partition root. > */ > static void compute_effective_cpumask(struct cpumask *new_cpus, > struct cpuset *cs, struct cpuset *parent) > { > - cpumask_and(new_cpus, cs->cpus_allowed, parent->effective_cpus); > + bool has_cpus; > + > + has_cpus = cpumask_and(new_cpus, cs->cpus_allowed, parent->effective_cpus); > + if (!has_cpus && is_in_v2_mode()) > + cpumask_copy(new_cpus, parent->effective_cpus); > +} > + > +/** > + * compute_effective_nodemask - Compute the effective nodemask of the cpuset > + * @new_cpus: the temp variable for the new effective_mems mask > + * @cs: the cpuset the need to recompute the new effective_mems mask > + * @parent: the parent cpuset > + * > + * For v2, the parent's effective_mems is inherited if nodemask empty. > + */ > +static void compute_effective_nodemask(nodemask_t *new_mems, > + struct cpuset *cs, struct cpuset *parent) > +{ > + bool has_mems; > + > + has_mems = nodes_and(*new_mems, cs->mems_allowed, parent->effective_mems); > + if (!has_mems && is_in_v2_mode()) > + nodes_copy(*new_mems, parent->effective_mems); > } > > /* > @@ -2148,15 +2171,6 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp, > goto update_parent_effective; > } > > - /* > - * If it becomes empty, inherit the effective mask of the > - * parent, which is guaranteed to have some CPUs unless > - * it is a partition root that has explicitly distributed > - * out all its CPUs. > - */ > - if (is_in_v2_mode() && !remote && cpumask_empty(tmp->new_cpus)) > - cpumask_copy(tmp->new_cpus, parent->effective_cpus); > - > /* > * Skip the whole subtree if > * 1) the cpumask remains the same, > @@ -2704,14 +2718,7 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems) > cpuset_for_each_descendant_pre(cp, pos_css, cs) { > struct cpuset *parent = parent_cs(cp); > > - bool has_mems = nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems); > - > - /* > - * If it becomes empty, inherit the effective mask of the > - * parent, which is guaranteed to have some MEMs. > - */ > - if (is_in_v2_mode() && !has_mems) > - *new_mems = parent->effective_mems; > + compute_effective_nodemask(new_mems, cp, parent); > > /* Skip the whole subtree if the nodemask remains the same. */ > if (nodes_equal(*new_mems, cp->effective_mems)) { > @@ -3923,7 +3930,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp) > > parent = parent_cs(cs); > compute_effective_cpumask(&new_cpus, cs, parent); > - nodes_and(new_mems, cs->mems_allowed, parent->effective_mems); > + compute_effective_nodemask(&new_mems, cs, parent); > > if (!tmp || !cs->partition_root_state) > goto update_tasks; > diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh > index 0d41aa0d343d..ca9bc38fdb95 100755 > --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh > +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh > @@ -495,13 +495,20 @@ REMOTE_TEST_MATRIX=( > # Narrowing cpuset.cpus to previously sibling-excluded CPUs should > # not return CPUs that were never actually owned. > " C1-4:P1 . C1-2:P1 C1-3:P2 . . \ > - . . . C3 . . p1:4|c11:1-2|c12:3 \ > + . . . C3 . . p1:4|c11:1-2|c12:3 \ > p1:P1|c11:P1|c12:P2 3" > # Expanding cpuset.cpus to include a previously sibling-excluded CPU > # after the sibling has become a member should correctly request it. > " C1-4:P1 . C1-2:P1 C1-3:P2 . . \ > - . . P0 C2-3 . . p1:1,4|c11:1|c12:2-3 \ > + . . P0 C2-3 . . p1:1,4|c11:1|c12:2-3 \ > p1:P1|c11:P0|c12:P2 2-3" > + # Cpusets with empty cpuset.cpus should inherit parent's effective_cpus > + " C1-4:P1 C5-6 C1-2 . C5 . \ > + . P1 P1 . . . p1:3-4|p2:5-6|c11:1-2|c12:3-4|c21:5|c22:5-6 \ > + p1:P1|p2:P1|c11:P1" > + " C1-4:P1 C5-6 C1-2 . C5 . \ > + . P1 P1 . O5=0 . p1:3-4|p2:6|c11:1-2|c12:3-4|c21:6|c22:6 \ > + p1:P1|p2:P1|c11:P1" > ) > > # LGTM. Reviewed-by: Ridong Chen -- Best regards Ridong