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=-8.3 required=3.0 tests=BAYES_00,DATE_IN_PAST_06_12, 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 CCFF3C4363A for ; Wed, 28 Oct 2020 22:30:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7262E2071A for ; Wed, 28 Oct 2020 22:30:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="31D5ynv4"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="VzXM6tXW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387646AbgJ1W37 (ORCPT ); Wed, 28 Oct 2020 18:29:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55598 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387570AbgJ1W30 (ORCPT ); Wed, 28 Oct 2020 18:29:26 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6A9C4C0613D2; Wed, 28 Oct 2020 15:29:26 -0700 (PDT) From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1603894382; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=CqSkQpMY6URuz0G0Q4TnfzC+8Rq7slmLYOYzQAzOWGc=; b=31D5ynv45XvdzRDTEELN87qhI/8dZPSaNTNTJOCAB47le0wvb6YrGebef1K6+R/yD/U6aU aZ64XufcS/VUufhS7Ix6k2Xdd/nsIwWTrOQMf1QxkAHv0VF+qOQygb1VZGNOUnEwAknB17 xZ2CrxmX+E4AELBSKoqbTUFaG3OuM3ZlDPxznTpQuXbTGUdIGacOtnmb13e1fJx6IBSKuC OhJpbARqtRuXXBOqZjh0a2y+lpPXH6A7pPv+nNAzKUKCF7M1fewCX05oSLRGX78+aldNf2 /PNLIH4ZgPav3aYvutCTrNdtRazco7kK/v1SHMy7J1oywJ3q/DP6BoFlCvGTeA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1603894382; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=CqSkQpMY6URuz0G0Q4TnfzC+8Rq7slmLYOYzQAzOWGc=; b=VzXM6tXWEg+XudQIjBFsQQy6kC9HVzTMeWbxvOMd5pYMok+TJDPH/B6ziFhpiKsdGF2Njk C3Ye3gLCeVxDAXCg== To: linux-block@vger.kernel.org Cc: Christoph Hellwig , Thomas Gleixner , David Runge , linux-rt-users@vger.kernel.org, Jens Axboe , linux-kernel@vger.kernel.org, Peter Zijlstra , Daniel Wagner , Sebastian Andrzej Siewior Subject: [PATCH 1/3] blk-mq: Don't complete on a remote CPU in force threaded mode Date: Wed, 28 Oct 2020 15:12:49 +0100 Message-Id: <20201028141251.3608598-1-bigeasy@linutronix.de> In-Reply-To: <20201028065616.GA24449@infradead.org> References: <20201028065616.GA24449@infradead.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org With force threaded interrupts enabled, raising softirq from an SMP function call will always result in waking the ksoftirqd thread. This is not optimal given that the thread runs at SCHED_OTHER priority. Completing the request in hard IRQ-context on PREEMPT_RT (which enforces the force threaded mode) is bad because the completion handler may acquire sleeping locks which violate the locking context. Disable request completing on a remote CPU in force threaded mode. Signed-off-by: Sebastian Andrzej Siewior --- block/blk-mq.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index 55bcee5dc0320..421a40968c9ff 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -648,6 +648,14 @@ static inline bool blk_mq_complete_need_ipi(struct req= uest *rq) if (!IS_ENABLED(CONFIG_SMP) || !test_bit(QUEUE_FLAG_SAME_COMP, &rq->q->queue_flags)) return false; + /* + * With force threaded interrupts enabled, raising softirq from an SMP + * function call will always result in waking the ksoftirqd thread. + * This is probably worse than completing the request on a different + * cache domain. + */ + if (force_irqthreads) + return false; =20 /* same CPU or cache domain? Complete locally */ if (cpu =3D=3D rq->mq_ctx->cpu || --=20 2.28.0