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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 83F63C433E0 for ; Sat, 16 Jan 2021 17:11:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5C9332388E for ; Sat, 16 Jan 2021 17:11:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728381AbhAPRKn (ORCPT ); Sat, 16 Jan 2021 12:10:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39102 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728256AbhAPRKg (ORCPT ); Sat, 16 Jan 2021 12:10:36 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7DA47C06138D for ; Sat, 16 Jan 2021 07:17:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=LVmTpyaDUYYU77ebxo6jkzUi32557khoLNpH/skJ208=; b=wERDfYvSXygoKCK80kbfKZw8hd 8uaeW0BzpJmQBXDckTiCLqYPef3sC6paHvutDzO1G44LIz9k8BqWJaHClKHJx8wp6c4ps78fh6l5F r9ZisDckgN4SKhiAHKFwKhbGxhppBq3JUpJL8uGCQvsg/9g2J+kzVcIiUxikjQnfuERmTMn5gZFfu 9FnOBjfuryhF5hG5j9Zh83vB/i4oebv6QYPhklkpQCK6Aql+1J25V4dU8xqru7yFkAdo05nPVAx2e IgzE56/Gvr0zHC0c+9oEZN/sMyqMMX5xZYfp/gdbZ/bLoOE9OcPPnh1B0L/bzvKUT2I++vg5v+Q3+ 6cgbBwuw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1l0nJa-00AOVx-FA; Sat, 16 Jan 2021 15:16:37 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id F12C43010CF; Sat, 16 Jan 2021 16:16:33 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D42BF202A3F5A; Sat, 16 Jan 2021 16:16:33 +0100 (CET) Date: Sat, 16 Jan 2021 16:16:33 +0100 From: Peter Zijlstra To: Lai Jiangshan Cc: Valentin Schneider , Ingo Molnar , Thomas Gleixner , LKML , Qian Cai , Vincent Donnefort , Dexuan Cui , "Paul E. McKenney" , Vincent Guittot , Steven Rostedt , Tejun Heo Subject: Re: [PATCH 3/4] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU Message-ID: References: <20210112144344.850850975@infradead.org> <20210112144843.849135905@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 16, 2021 at 10:45:04PM +0800, Lai Jiangshan wrote: > On Sat, Jan 16, 2021 at 8:45 PM Peter Zijlstra wrote: > > It is also the exact sequence normal per-cpu threads (smpboot) use to > > preserve affinity. > > Other per-cpu threads normally do short-live works. wq's work can be > lengthy, cpu-intensive, heavy-lock-acquiring or even call > get_online_cpus() which might result in a deadlock with kthread_park(). kthread_park() is called by the migration thread running the workqueue_online_cpu() callback. kthread_parkme() is called by the worker thread, after it completes a work and has no locks held from that context.