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,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 D1285C433E0 for ; Thu, 21 May 2020 20:01:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B0C0E20748 for ; Thu, 21 May 2020 20:01:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730195AbgEUUA5 (ORCPT ); Thu, 21 May 2020 16:00:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50570 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729780AbgEUUA5 (ORCPT ); Thu, 21 May 2020 16:00:57 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EA9A1C061A0E; Thu, 21 May 2020 13:00:56 -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 1jbrMP-0008Jj-44; Thu, 21 May 2020 22:00:09 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 57046100C2D; Thu, 21 May 2020 22:00:08 +0200 (CEST) From: Thomas Gleixner To: Jens Axboe , Ming Lei Cc: Christoph Hellwig , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, John Garry , Bart Van Assche , Hannes Reinecke , io-uring@vger.kernel.org, Peter Zijlstra Subject: Re: io_uring vs CPU hotplug, was Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request_hctx In-Reply-To: <15f9f975-1baf-dc90-5730-00df08829523@kernel.dk> References: <20200520011823.GA415158@T590> <20200520030424.GI416136@T590> <20200520080357.GA4197@lst.de> <8f893bb8-66a9-d311-ebd8-d5ccd8302a0d@kernel.dk> <448d3660-0d83-889b-001f-a09ea53fa117@kernel.dk> <87tv0av1gu.fsf@nanos.tec.linutronix.de> <2a12a7aa-c339-1e51-de0d-9bc6ced14c64@kernel.dk> <87eereuudh.fsf@nanos.tec.linutronix.de> <20200521022746.GA730422@T590> <87367tvh6g.fsf@nanos.tec.linutronix.de> <20200521092340.GA751297@T590> <87pnaxt9nv.fsf@nanos.tec.linutronix.de> <15f9f975-1baf-dc90-5730-00df08829523@kernel.dk> Date: Thu, 21 May 2020 22:00:08 +0200 Message-ID: <87k115t5x3.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 Jens Axboe writes: > Again, this is mixing up io_uring and blk-mq. Maybe it's the fact that > both use 'ctx' that makes this confusing. On the blk-mq side, the 'ctx' > is the per-cpu queue context, for io_uring it's the io_uring instance. Yes, that got me horribly confused. :) > io_sq_thread() doesn't care about any sort of percpu mappings, it's > happy as long as it'll keep running regardless of whether or not the > optional pinned CPU is selected and then offlined. Fair enough. So aside of the potential spin forever if the uring thread is lifted to an RT scheduling class, this looks all good. Though I assume that if that thread is pinned and an admin pushs it into RT scheduling the spinning live lock can happen independent of cpu hotplug. Thanks, tglx