From patchwork Tue Oct 8 11:24:57 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chen Ridong X-Patchwork-Id: 13826319 Received: from dggsgout11.his.huawei.com (dggsgout11.his.huawei.com [45.249.212.51]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 785A41DED4C; Tue, 8 Oct 2024 11:33:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.51 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728387215; cv=none; b=JzVXu4Lf6/T+srS+W/R0zZpGWJZIFvDlRAheMJLppWjWlT5hqsZEAMqwckA4Uc50GUGA0JsyPaGOpYqGc4OkR5QrZroCoqgYaDMHnvXnjHkWorsHs+4yxW7nx1feU66l2PF6ahdAhTdSDVfmGhOgV7KACevNPyOVGfqtQPMnVIc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728387215; c=relaxed/simple; bh=r52NoDC0OdcgHEGx6rJiBaq4EWHBLJdtHAloZ1U4kKo=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=MUpaRxP/3Lhy44FiI2/VgKKiupcoDkW6QX0KKMjiazzHHHDTrwwW73OjHj6AA6qTHER5dZzQam2YJFvNecdEwOOUgCy9aY0JGZgU/8mn/UZJA8rG9C4PChihub+bdgiiuqKIic8/1mRbFGDm6fImueyw0Uk7yURmiN7fO7TT8sY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=pass smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=45.249.212.51 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.93.142]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4XNDRC2Kk4z4f3l20; Tue, 8 Oct 2024 19:33:11 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id C91E81A07BA; Tue, 8 Oct 2024 19:33:28 +0800 (CST) Received: from hulk-vt.huawei.com (unknown [10.67.174.121]) by APP4 (Coremail) with SMTP id gCh0CgAnqMRuGAVnI_ERDg--.13677S4; Tue, 08 Oct 2024 19:33:28 +0800 (CST) From: Chen Ridong To: martin.lau@linux.dev, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, tj@kernel.org, lizefan.x@bytedance.com, hannes@cmpxchg.org, roman.gushchin@linux.dev, mkoutny@suse.com Cc: bpf@vger.kernel.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, chenridong@huawei.com Subject: [PATCH v6 2/3] workqueue: doc: Add a note saturating the system_wq is not permitted Date: Tue, 8 Oct 2024 11:24:57 +0000 Message-Id: <20241008112458.49387-3-chenridong@huaweicloud.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20241008112458.49387-1-chenridong@huaweicloud.com> References: <20241008112458.49387-1-chenridong@huaweicloud.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CM-TRANSID: gCh0CgAnqMRuGAVnI_ERDg--.13677S4 X-Coremail-Antispam: 1UD129KBjvJXoW7Aw1xGF13Cw48Cw4DKFyxuFg_yoW8JFy3pr W3CFyav3WxJr12ka4kXr47WFy7GF18GFsrGFs7tw1IvFn8A3s7Kw4xKryrta4DJr95uFW8 ZFZ2v3s0y34jvrUanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUP2b4IE77IF4wAFF20E14v26rWj6s0DM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28IrcIa0xkI8VA2jI8067AKxVWUXw A2048vs2IY020Ec7CjxVAFwI0_Xr0E3s1l8cAvFVAK0II2c7xJM28CjxkF64kEwVA0rcxS w2x7M28EF7xvwVC0I7IYx2IY67AKxVW5JVW7JwA2z4x0Y4vE2Ix0cI8IcVCY1x0267AKxV W8Jr0_Cr1UM28EF7xvwVC2z280aVAFwI0_GcCE3s1l84ACjcxK6I8E87Iv6xkF7I0E14v2 6rxl6s0DM2AIxVAIcxkEcVAq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40Ex7xfMc Ij6xIIjxv20xvE14v26r106r15McIj6I8E87Iv67AKxVWUJVW8JwAm72CE4IkC6x0Yz7v_ Jr0_Gr1lF7xvr2IYc2Ij64vIr41lFIxGxcIEc7CjxVA2Y2ka0xkIwI1lc7CjxVAaw2AFwI 0_GFv_Wryl42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG 67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r4a6rW5MI IYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E 14v26F4j6r4UJwCI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_Jr 0_Gr1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7IU0jN t3UUUUU== X-CM-SenderInfo: hfkh02xlgr0w46kxt4xhlfz01xgou0bp/ From: Chen Ridong If something is expected to generate large number of concurrent works, it should utilize its own dedicated workqueue rather than system wq. Because this may saturate system_wq and potentially block other's works. eg, cgroup release work. Let's document this as a note. Signed-off-by: Chen Ridong --- Documentation/core-api/workqueue.rst | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst index 16f861c9791e..2b813f80ce39 100644 --- a/Documentation/core-api/workqueue.rst +++ b/Documentation/core-api/workqueue.rst @@ -357,6 +357,11 @@ Guidelines difference in execution characteristics between using a dedicated wq and a system wq. + Note: If something may generate more than @max_active outstanding + work items (do stress test your producers), it may saturate a system + wq and potentially lead to deadlock. It should utilize its own + dedicated workqueue rather than the system wq. + * Unless work items are expected to consume a huge amount of CPU cycles, using a bound wq is usually beneficial due to the increased level of locality in wq operations and work item execution.