From patchwork Fri Oct 23 11:04:00 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sebastian Andrzej Siewior X-Patchwork-Id: 286898 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=-9.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED autolearn=unavailable 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 23704C55179 for ; Fri, 23 Oct 2020 11:04:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C14C821D43 for ; Fri, 23 Oct 2020 11:04:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="VU/I/Bg0"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="UnEzQ4M/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S462706AbgJWLEE (ORCPT ); Fri, 23 Oct 2020 07:04:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54026 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S462548AbgJWLED (ORCPT ); Fri, 23 Oct 2020 07:04:03 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A242C0613CE; Fri, 23 Oct 2020 04:04:03 -0700 (PDT) Date: Fri, 23 Oct 2020 13:04:00 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1603451041; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=j1o05ovjntirIj7cvm7bSPa5eySCqPWLuUvFBBxTkcA=; b=VU/I/Bg0fjftmhfkNoiTI5iQAkWt1oroH4F41nG/CTl2uJHdNhPckdnBQqbVas1E1ON0pK yWtYg+1sxh8pnuRX09q7grhMA5ExKHvEq4tUlD5e4PmTGZD8eILAiC50zsA2xoekbuC7GI V7Et6fYnqpFWlxEW8NaEqob68BlhofnBfRLmNmF9Vgd4t2YrRsDVn9saDXGfeMGxf6PvL9 HcBqVwWt7NPl1ot8NBdkEbY9q7Ah/hgACZz+zThD4LBIcE5pNr69pdBISg+FwQp/IplXRh u0UcS7rrdehouC3VUYfoOc3rjBpHD9hmVL6CFsG1G8xBvaXus7B2u+obpb2uUQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1603451041; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=j1o05ovjntirIj7cvm7bSPa5eySCqPWLuUvFBBxTkcA=; b=UnEzQ4M/+js0ciQkn+pulvrti1+fg2aEU1ycvfsSoEgkxQxIRZJkVTxbb25CBaUFmUS6MF hm4LzqNXplO2z+DQ== From: Sebastian Andrzej Siewior To: David Runge Cc: linux-rt-users@vger.kernel.org, Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Thomas Gleixner , Daniel Wagner Subject: [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT Message-ID: <20201023110400.bx3uzsb7xy5jtsea@linutronix.de> References: <20201021175059.GA4989@hmbx> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201021175059.GA4989@hmbx> Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org blk_mq_complete_request_remote() will dispatch request completion to another CPU via IPI if the CPU belongs to a different cache domain. This breaks on PREEMPT_RT because the IPI function will complete the request in IRQ context which includes acquiring spinlock_t typed locks. Completing the IPI request in softirq on the remote CPU is probably less efficient because it would require to wake ksoftirqd for this task (which runs at SCHED_OTHER). Ignoring the IPI request and completing the request locally is probably the best option. It be completed either in the IRQ-thread or at the end of the routine in softirq context. Let blk_mq_complete_need_ipi() return that there is no need for IPI on PREEMPT_RT. Signed-off-by: Sebastian Andrzej Siewior --- block/blk-mq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index e37aa31332b70..99d2fb51e0e84 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -647,7 +647,7 @@ static inline bool blk_mq_complete_need_ipi(struct request *rq) { int cpu = raw_smp_processor_id(); - if (!IS_ENABLED(CONFIG_SMP) || + if (!IS_ENABLED(CONFIG_SMP) || IS_ENABLED(CONFIG_PREEMPT_RT) || !test_bit(QUEUE_FLAG_SAME_COMP, &rq->q->queue_flags)) return false;