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([2601:188:c102:b180:1f8b:71d0:77b1:1f6e]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-88060db5a9esm9423726d6.1.2025.11.03.13.17.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Nov 2025 13:17:47 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <6911f3c8-dcef-444f-bea2-d6bb247563d9@redhat.com> Date: Mon, 3 Nov 2025 16:17:46 -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: [cgroup/for-6.19 PATCH 3/3] cgroup/cpuset: Globally track isolated_cpus update To: Chen Ridong , Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Chen Ridong , Gabriele Monaco , Frederic Weisbecker References: <20251103013411.239610-1-longman@redhat.com> <20251103013411.239610-4-longman@redhat.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 11/3/25 1:46 AM, Chen Ridong wrote: > > On 2025/11/3 9:34, Waiman Long wrote: >> The current cpuset code passes a local isolcpus_updated flag around in a >> number of functions to determine if external isolation related cpumasks >> like wq_unbound_cpumask should be updated. It is a bit cumbersome and >> makes the code more complex. Simplify the code by using a global boolean > Agree. > >> flag "isolated_cpus_updating" to track this. This flag will be set in >> isolated_cpus_update() and cleared in update_isolation_cpumasks(). >> >> No functional change is expected. >> >> Signed-off-by: Waiman Long >> --- >> kernel/cgroup/cpuset.c | 74 ++++++++++++++++++++---------------------- >> 1 file changed, 35 insertions(+), 39 deletions(-) >> >> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c >> index d6d459c95d82..406a1c3789f5 100644 >> --- a/kernel/cgroup/cpuset.c >> +++ b/kernel/cgroup/cpuset.c >> @@ -81,6 +81,13 @@ static cpumask_var_t subpartitions_cpus; >> */ >> static cpumask_var_t isolated_cpus; >> > Is isolated_cpus protected by cpuset_mutex or callback_lock? > > If isolated_cpus is indeed protected by cpuset_mutex, perhaps we can move the update of > isolated_cpus outside the critical section of callback_lock. This would allow us to call > update_isolation_cpumasks in isolated_cpus_update, making the isolated_cpus_updating variable > unnecessary. Reducing a global variable would be beneficial. isolated_cpus is a user visible cpumask. So I would like to protect it with both cpuset_mutex and callback_lock like the other user visible cpumasks. > >> +/* >> + * isolated_cpus updating flag (protected by cpuset_mutex) >> + * Set if isolated_cpus is going to be updated in the current >> + * cpuset_mutex crtical section. >> + */ >> +static bool isolated_cpus_updating; >> + >> /* >> * Housekeeping (HK_TYPE_DOMAIN) CPUs at boot >> */ >> @@ -1327,13 +1334,14 @@ static void isolated_cpus_update(int old_prs, int new_prs, struct cpumask *xcpus >> cpumask_or(isolated_cpus, isolated_cpus, xcpus); >> else >> cpumask_andnot(isolated_cpus, isolated_cpus, xcpus); >> + >> + isolated_cpus_updating = true; >> } >> >> /* >> * isolated_cpus_should_update - Returns if the isolated_cpus mask needs update >> * @prs: new or old partition_root_state >> * @parent: parent cpuset >> - * Return: true if isolated_cpus needs modification, false otherwise >> */ >> static bool isolated_cpus_should_update(int prs, struct cpuset *parent) >> { >> @@ -1347,15 +1355,12 @@ static bool isolated_cpus_should_update(int prs, struct cpuset *parent) >> * @new_prs: new partition_root_state >> * @parent: parent cpuset >> * @xcpus: exclusive CPUs to be added >> - * Return: true if isolated_cpus modified, false otherwise >> * >> * Remote partition if parent == NULL >> */ >> -static bool partition_xcpus_add(int new_prs, struct cpuset *parent, >> +static void partition_xcpus_add(int new_prs, struct cpuset *parent, >> struct cpumask *xcpus) >> { >> - bool isolcpus_updated; >> - >> WARN_ON_ONCE(new_prs < 0); >> lockdep_assert_held(&callback_lock); >> if (!parent) >> @@ -1365,13 +1370,11 @@ static bool partition_xcpus_add(int new_prs, struct cpuset *parent, >> if (parent == &top_cpuset) >> cpumask_or(subpartitions_cpus, subpartitions_cpus, xcpus); >> >> - isolcpus_updated = (new_prs != parent->partition_root_state); >> - if (isolcpus_updated) >> + if (new_prs != parent->partition_root_state) > Can this if statement be replaced with new helper isolated_cpus_should_update？ The isolated_cpus_should_update() helper is for validating the change. It is too late to call in partition_xcpus_add/del(). Cheers, Longman