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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 31/33] kthread: Comment on the purpose and placement of kthread_affine_node() call Date: Sun, 25 Jan 2026 23:45:38 +0100 Message-ID: <20260125224541.50226-32-frederic@kernel.org> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20260125224541.50226-1-frederic@kernel.org> References: <20260125224541.50226-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 984EC40005 X-Rspamd-Server: rspam07 X-Stat-Signature: xcorpcmn7aetf7zcb3ggbpmn8hmjtg3f X-HE-Tag: 1769381405-766934 X-HE-Meta: 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 IH6IRIkm sQC94N5uy3me1M2pxiuFKSoo2VIYN4OSxmKlDNVH6WBSD3ib9iZU0dQeFIrwCeW3vpsbrnFfCGCXiJ9Q+ov2pJRBEL1RVOMclDtFziedIj790BdovxwERJ0gAh+mF4e9gud+kw+ePd+Oizs6cMo8z8I95qa3mqjybt4N+h253Z3ItQsI8kwq5XZ5uapYlWpVE3Mik3XsTQ+ML/6SBuJ+RVS+Eb9GOHCmhaFyl2xJ5/W7YfG2YiKAI+EUrxgjCgjRl21cQ7O8cFbP6KeEP8GLm+ERX5BTm0rS2RZyOtrq30Z4fGZVgC5Y5oHhdx7mhCGL6VksewSMxt6oeKwtVy8uXYbnvcA== 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 03008154249c..51f419139dea 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(); -- 2.51.1