From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1AAC5CCD185 for ; Mon, 13 Oct 2025 20:35:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=o2RaB4lHHhlKa+8v8iZE0Fllt8dt+Sn1Sj5thp5J+H4=; b=bjNzhxmAuXZSd9jUrMDZBFv+CM 45uVk+BsbV0JwhW0qTDG7/bAW97ANP0qhSbHTbUyhOPaPQmRb1iT8y2agVvV/pxWJhBJcM14XkkVY rIVSRAh6YzbVkUoSOnquabUf4P5DfXW8wA7LScbWjP39XIfE4sMA5K8SAbV86KREyh0Kd1kjO6e4m xjnT/NKVHZQEziU0HNEBoAWdSg7ot3Gw7NNaq2xGzSJypnMgxhV2+hSo6cIuR4bOmip1kHUXKRaow iy6f2jNHFdQXzBntEAqsYhJTWdJv1VlNRD9IIeWJHue2W3CrY8tUfpY2cVCYp9Vl+NrnYK4KH2CF7 0T2yiJcA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1v8PGh-0000000EPzH-45dB; Mon, 13 Oct 2025 20:35:43 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1v8PGg-0000000EPx9-15c7 for linux-arm-kernel@lists.infradead.org; Mon, 13 Oct 2025 20:35:43 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id E5AE44374F; Mon, 13 Oct 2025 20:35:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 858D8C4CEE7; Mon, 13 Oct 2025 20:35:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1760387741; bh=n52cAu7bEMYLK1x1CARbNE9gVHxK/1DrMBlj3TyiG6U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Hwx+RCh+ZncRTZW4J3H101zxwGK2eXC7I/AqUiWKIv2Duuwwy39jB7rQi4ZnPKStV AbZRbdrU5REoIKByt/LVOaIEFYsTkgcDK/rQsCPMoITkhkdZg7ALJytPyN7MOI1vc+ RT2iSlPvYNcvFM6/vFKmR2bKzL+SNzPQURqdZYp7huxAcjMbS59DbwOQUz7/bpVVj0 HlKhsXGjIBcqreM/spUfVwgtUf7zzM7ao5qVaRVLlRlbKWfKCo1/4m/YIzCT1UeKOQ h3AAzzYPrXCd+VjamYW07Z5gyLAAw3SuDh1Wkx20np8piV10n7YbOohjL426Rqpvuk +nJqSOrG0UW6A== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Andrew Morton , Bjorn Helgaas , Catalin Marinas , Danilo Krummrich , "David S . 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-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251013_133542_327158_1CE69DCF X-CRM114-Status: GOOD ( 13.36 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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