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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: Wed, 24 Dec 2025 14:45:18 +0100 Message-ID: <20251224134520.33231-32-frederic@kernel.org> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20251224134520.33231-1-frederic@kernel.org> References: <20251224134520.33231-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 270FF20011 X-Stat-Signature: 66wo3airkty35gzysmjsfw8ijgsxjw57 X-Rspam-User: X-HE-Tag: 1766584197-557449 X-HE-Meta: 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 hacm0oXz N9NGfT/TYjtvOHUc= 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