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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 CC3DAC433E0 for ; Mon, 18 May 2020 18:38:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B0D3020715 for ; Mon, 18 May 2020 18:38:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728657AbgERSiU (ORCPT ); Mon, 18 May 2020 14:38:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40434 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728626AbgERSiU (ORCPT ); Mon, 18 May 2020 14:38:20 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E6DA6C061A0C for ; Mon, 18 May 2020 11:38:19 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jakeL-00020C-2n; Mon, 18 May 2020 20:38:05 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 832CA100606; Mon, 18 May 2020 20:38:04 +0200 (CEST) From: Thomas Gleixner To: Christoph Hellwig , Ming Lei Cc: Christoph Hellwig , linux-block@vger.kernel.org, John Garry , Bart Van Assche , Hannes Reinecke Subject: Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request_hctx In-Reply-To: <20200518165619.GA17465@lst.de> References: <20200518093155.GB35380@T590> <87imgty15d.fsf@nanos.tec.linutronix.de> <20200518115454.GA46364@T590> <20200518131634.GA645@lst.de> <20200518141107.GA50374@T590> <20200518165619.GA17465@lst.de> Date: Mon, 18 May 2020 20:38:04 +0200 Message-ID: <87o8qlw0kz.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Christoph Hellwig writes: > On Mon, May 18, 2020 at 10:11:07PM +0800, Ming Lei wrote: >> On Mon, May 18, 2020 at 03:16:34PM +0200, Christoph Hellwig wrote: >> > On Mon, May 18, 2020 at 07:54:54PM +0800, Ming Lei wrote: >> > > >> > > I guess I misunderstood your point, sorry for that. >> > > >> > > The requirement is just that the request needs to be allocated on one online >> > > CPU after INACTIVE is set, and we can use a workqueue to do that. >> > >> > I've looked over the code again, and I'm really not sure why we need that. >> > Presumable the CPU hotplug code ensures tasks don't get schedule on the >> > CPU running the shutdown state machine, so if we just do a retry of the >> >> percpu kthread still can be scheduled on the cpu to be online, see >> is_cpu_allowed(). And bound wq has been used widely in fs code. > > s/to be online/to be offlined/ I guess. > > Shouldn't all the per-cpu kthreads also stop as part of the offlining? > If they don't quiesce before the new blk-mq stop state I think we need > to make sure they do. It is rather pointless to quiesce the requests > if a thread that can submit I/O is still live. Which kthreads are you talking about? Workqueues? CPU bound workqueues are shut down in CPUHP_AP_WORKQUEUE_ONLINE state. Thanks, tglx