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([2601:188:c102:b180:1f8b:71d0:77b1:1f6e]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4ede87e2a78sm14921cf.22.2025.11.12.12.18.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Nov 2025 12:18:18 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <3c449d75-2a44-4acc-b3f6-0b2c261db1bd@redhat.com> Date: Wed, 12 Nov 2025 15:18:16 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v2 02/22] cpuset: add early empty cpumask check in partition_xcpus_add/del To: Chen Ridong , tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, lujialin4@huawei.com, chenridong@huawei.com References: <20251025064844.495525-1-chenridong@huaweicloud.com> <20251025064844.495525-3-chenridong@huaweicloud.com> Content-Language: en-US In-Reply-To: <20251025064844.495525-3-chenridong@huaweicloud.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/25/25 2:48 AM, Chen Ridong wrote: > From: Chen Ridong > > Add a check for an empty cpumask at the start of partition_xcpus_add() > and partition_xcpus_del(). This allows the functions to return early, > avoiding unnecessary computation when there is no work to be done. > > Signed-off-by: Chen Ridong > --- > kernel/cgroup/cpuset.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 6af4d80b53c4..3ba9ca4e8f5e 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -1345,6 +1345,9 @@ static bool partition_xcpus_add(int new_prs, struct cpuset *parent, > > WARN_ON_ONCE(new_prs < 0); > lockdep_assert_held(&callback_lock); > + if (cpumask_empty(xcpus)) > + return false; > + > if (!parent) > parent = &top_cpuset; > > @@ -1377,6 +1380,9 @@ static bool partition_xcpus_del(int old_prs, struct cpuset *parent, > > WARN_ON_ONCE(old_prs < 0); > lockdep_assert_held(&callback_lock); > + if (cpumask_empty(xcpus)) > + return false; > + > if (!parent) > parent = &top_cpuset; > partition_xcpus_add() and partition_xcpus_del() are supposed to be called only when action is really needed. The empty xcpus check should be done earlier to avoid calling them in the first  place. So unless you are planning to change the logic that they will always be called even if action is not really needed. If so, you have to state in the commit log. Cheers, Longman