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=-3.9 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 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 54A0AC388F9 for ; Fri, 23 Oct 2020 13:52:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EFD8320936 for ; Fri, 23 Oct 2020 13:52:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="fdzB5UuF"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="drGgKFg3" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750129AbgJWNwY (ORCPT ); Fri, 23 Oct 2020 09:52:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52012 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750124AbgJWNwX (ORCPT ); Fri, 23 Oct 2020 09:52:23 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D1CB2C0613CE; Fri, 23 Oct 2020 06:52:22 -0700 (PDT) Date: Fri, 23 Oct 2020 15:52:19 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1603461141; 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=9mSwLBiQN8wgOA1EFVT7t2Fh/mBpsT8gU/jlnEuQWt8=; b=fdzB5UuFFowfwPRMWd5yX43uPmKAxvOXRixse6gFs8C6jHd8FGLFrKm5x4reeeUWp7O56t sqe/0MlfnTUDc6r6f/unMp7HWgBU7db+F239GI2xl4UZDYEda8FrIX+xkOuRZKO8cAv1gK IafvRjj0x3j1cnlBX7nxyNOe+kwvsG6XiIAQ+0YwFeQpBo25RFgZdn35biaArgq7gYr9hX YrzPo3h5/HKaGKe/bnTXrOXyZgmw2NvN3Uy8E1itkvjiQ+vXa9y24ZETR0PmZVfWw+CmrU j61B/IwQodzy3wxYrHIIB1j6n6s2zpPeNSgl3PGocufv34QHB0mwq46flA68dg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1603461141; 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=9mSwLBiQN8wgOA1EFVT7t2Fh/mBpsT8gU/jlnEuQWt8=; b=drGgKFg3WTRVPkBaGDa+ttUhbedrrsoR19jaWdrA52t4mnhMJyKF433463bINPKtAr0UsM 14d3ln1cB9U/6vBQ== From: Sebastian Andrzej Siewior To: Christoph Hellwig Cc: David Runge , 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: Re: [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT Message-ID: <20201023135219.mzzl76eqqy6tqwhe@linutronix.de> References: <20201021175059.GA4989@hmbx> <20201023110400.bx3uzsb7xy5jtsea@linutronix.de> <20201023112130.GA23790@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201023112130.GA23790@infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On 2020-10-23 12:21:30 [+0100], Christoph Hellwig wrote: > > - 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)) > > This needs a big fat comment explaining your rationale. And probably > a separate if statement to make it obvious as well. Okay. How much difference does it make between completing in-softirq vs in-IPI? I'm asking because acquiring a spinlock_t in an IPI shouldn't be done (as per Documentation/locking/locktypes.rst). We don't have anything in lockdep that will complain here on !RT and we the above we avoid the case on RT. Sebastian