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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: Thu, 1 Jan 2026 23:13:56 +0100 Message-ID: <20260101221359.22298-32-frederic@kernel.org> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20260101221359.22298-1-frederic@kernel.org> References: <20260101221359.22298-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 3865B180006 X-Stat-Signature: jz137hak8hc4y366uhmsefyf6zkufj6h X-Rspam-User: X-HE-Tag: 1767305909-577833 X-HE-Meta: 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 XHduivWK tOeSvx4CMI3goS14QKFnWS+FixvDSRYVp+qccnvYVMx0sUcDPZjPaCpJ+gLzDRHwg/+sZ9rRNtWidOi/pYGmL4OggrAz/V+jABP2MkgD5buPkzFfmOygymWJ0z19fux1ri39H+l2OJ+An/LbSgMN96suhRqhLUZnMkPKC67n7PzUPCJ6O4PczPjIar+F3O4+vSs46eEC1+gE2H2r3BQ5gw4efYs4G9EJYutWG1ZwWf7ZiSbr7r+fsDr86lmysZZiDC9/x3gMuG/zC8uiQPb3qH8aeYwZMO7Cqe+TyHM1fuBXifljV4ui8DN9KrNmEUohFBBZpvEBBHRzNaVs8YdVVv+RVmw== 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