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Miller" , Eric Dumazet , Gabriele Monaco , Greg Kroah-Hartman , Ingo Molnar , Jakub Kicinski , Jens Axboe , Johannes Weiner , Lai Jiangshan , Marco Crivellari , Michal Hocko , Muchun Song , Paolo Abeni , Peter Zijlstra , Phil Auld , "Rafael J . Wysocki" , Roman Gushchin , Shakeel Butt , Simon Horman , Tejun Heo , Thomas Gleixner , Vlastimil Babka , Waiman Long , Will Deacon , cgroups@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-block@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH 30/33] kthread: Add API to update preferred affinity on kthread runtime Date: Mon, 13 Oct 2025 22:31:43 +0200 Message-ID: <20251013203146.10162-31-frederic@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251013203146.10162-1-frederic@kernel.org> References: <20251013203146.10162-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: he6u494mcoi4kw3aeazmojcc16z7416y X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 824D240008 X-HE-Tag: 1760387750-294274 X-HE-Meta: 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 YY8Ts1Lv 4dbDzj1E++nLYeG6aX/PLMxoW6Hfw7byus6xuACJ45k98M4QkqGdVzuP+rWsDNtrFndRjgpIMwCaqC6IqFQyLUmNhgPAFCxqCmawHiH3Y2X5WqB2okqR4MDOJ353ECvlwnoeKWDJ+Pv9pJ8AS9NqoFqBEiP3kJJGLtghFFgGm8LlTO6DOaCx01xJbxWrFLa+UYsa8bFt6Jf++EL0NLTGYSQKEqTixSh0dzz3unULVbbd7mVnHOqtDHW/5ybh4e+o9EmKARWlNiQ4aK2A= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Kthreads can apply for a preferred affinity upon creation but they have no means to update that preferred affinity after the first wake up. kthread_affine_preferred() is optimized by assuming the kthread is sleeping while applying the allowed cpumask. Therefore introduce a new API to further update the preferred affinity. It will be used by IRQ kthreads. Signed-off-by: Frederic Weisbecker --- include/linux/kthread.h | 1 + kernel/kthread.c | 55 +++++++++++++++++++++++++++++++++++------ 2 files changed, 48 insertions(+), 8 deletions(-) diff --git a/include/linux/kthread.h b/include/linux/kthread.h index c92c1149ee6e..a06cae7f2c55 100644 --- a/include/linux/kthread.h +++ b/include/linux/kthread.h @@ -86,6 +86,7 @@ void free_kthread_struct(struct task_struct *k); void kthread_bind(struct task_struct *k, unsigned int cpu); void kthread_bind_mask(struct task_struct *k, const struct cpumask *mask); int kthread_affine_preferred(struct task_struct *p, const struct cpumask *mask); +int kthread_affine_preferred_update(struct task_struct *p, const struct cpumask *mask); int kthread_stop(struct task_struct *k); int kthread_stop_put(struct task_struct *k); bool kthread_should_stop(void); diff --git a/kernel/kthread.c b/kernel/kthread.c index d36bdfbd004e..f3397cf7542a 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -322,17 +322,16 @@ EXPORT_SYMBOL_GPL(kthread_parkme); void __noreturn kthread_exit(long result) { struct kthread *kthread = to_kthread(current); + struct cpumask *to_free = NULL; kthread->result = result; - if (!list_empty(&kthread->affinity_node)) { - mutex_lock(&kthread_affinity_lock); - list_del(&kthread->affinity_node); - mutex_unlock(&kthread_affinity_lock); - if (kthread->preferred_affinity) { - kfree(kthread->preferred_affinity); - kthread->preferred_affinity = NULL; - } + scoped_guard(mutex, &kthread_affinity_lock) { + if (!list_empty(&kthread->affinity_node)) + list_del_init(&kthread->affinity_node); + to_free = kthread->preferred_affinity; + kthread->preferred_affinity = NULL; } + kfree(to_free); do_exit(0); } EXPORT_SYMBOL(kthread_exit); @@ -900,6 +899,46 @@ int kthread_affine_preferred(struct task_struct *p, const struct cpumask *mask) } EXPORT_SYMBOL_GPL(kthread_affine_preferred); +/** + * kthread_affine_preferred_update - update a kthread's preferred affinity + * @p: thread created by kthread_create(). + * @cpumask: new mask of CPUs (might not be online, must be possible) for @k + * to run on. + * + * Update the cpumask of the desired kthread's affinity that was passed by + * a previous call to kthread_affine_preferred(). This can be called either + * before or after the first wakeup of the kthread. + * + * Returns 0 if the affinity has been applied. + */ +int kthread_affine_preferred_update(struct task_struct *p, + const struct cpumask *mask) +{ + struct kthread *kthread = to_kthread(p); + cpumask_var_t affinity; + int ret = 0; + + if (!zalloc_cpumask_var(&affinity, GFP_KERNEL)) + return -ENOMEM; + + scoped_guard(mutex, &kthread_affinity_lock) { + if (WARN_ON_ONCE(!kthread->preferred_affinity || + list_empty(&kthread->affinity_node))) { + ret = -EINVAL; + goto out; + } + + cpumask_copy(kthread->preferred_affinity, mask); + kthread_fetch_affinity(kthread, affinity); + set_cpus_allowed_ptr(p, affinity); + } +out: + free_cpumask_var(affinity); + + return ret; +} +EXPORT_SYMBOL_GPL(kthread_affine_preferred_update); + static int kthreads_update_affinity(bool force) { cpumask_var_t affinity; -- 2.51.0