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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 29/33] kthread: Comment on the purpose and placement of kthread_affine_node() call Date: Mon, 13 Oct 2025 22:31:42 +0200 Message-ID: <20251013203146.10162-30-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-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: D867420007 X-Stat-Signature: 33hm3e1h1kxwzgqm9jk5fnm61iohgt65 X-Rspam-User: X-HE-Tag: 1760387742-668283 X-HE-Meta: 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 DKwUWn3f uOtRioGf9VBB+p8rKH4fMrG08NCUS5tt1a8frE5E7kjyU1chuMC08SqKAQ5gV8kJhuBvAmDGs65nTxpJf2OKr2tLVQkUFcoLd8haj6OJkgO8Zq+VNows7590fUGyk85fYPedK4PoQKg9Hpu7WgjCFkWA06g8xykRyWTfVQssbJ7UwotLysjgSp8bebr8mFW1DjhMQYHRpOnaZd1dp0H7ySnYwbAk7R7IRzIejpxvHWZWTqDt+RO6TCIVfE75zM+H5NjsWSc8GILu8iKLvYe++bedW/5K7+9RpRM5s4kLwmWPJav7TqObbd+H01cLMUHtLEhkenmbA7BmImk7yeyei/+NOvA== 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: It may not appear obvious why kthread_affine_node() is not called before the kthread creation completion instead of after the first wake-up. The reason is that kthread_affine_node() applies a default affinity behaviour that only takes place if no affinity preference have already been passed by the kthread creation call site. Add a comment to clarify that. Reported-by: Peter Zijlstra Signed-off-by: Frederic Weisbecker --- kernel/kthread.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/kthread.c b/kernel/kthread.c index 4d3cc04e5e8b..d36bdfbd004e 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -453,6 +453,10 @@ static int kthread(void *_create) self->started = 1; + /* + * Apply default node affinity if no call to kthread_bind[_mask]() nor + * kthread_affine_preferred() was issued before the first wake-up. + */ if (!(current->flags & PF_NO_SETAFFINITY) && !self->preferred_affinity) kthread_affine_node(); -- 2.51.0