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=-5.8 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 5743CC433E6 for ; Tue, 26 Jan 2021 20:13:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 07A1022241 for ; Tue, 26 Jan 2021 20:13:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726668AbhAZFYn (ORCPT ); Tue, 26 Jan 2021 00:24:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43018 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727270AbhAYKAN (ORCPT ); Mon, 25 Jan 2021 05:00:13 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 339FBC0617A9; Mon, 25 Jan 2021 00:33:26 -0800 (PST) Date: Mon, 25 Jan 2021 09:30:29 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1611563429; 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=fT0yLbgSHXoqxC+Ppvc+ZiBYpclK9xLccUp9T4OyAhY=; b=BemnhpDaK7krGlakrswG4b/fJb0d7BgwDGu88JGO2M+isSnyVoDKEmoMM6aSV0B0LOABcF KizpKLGwv2O49+9JMQRYLbM6MSz9FbJZJkryfJewzhBzkp90pWv2MQPychF7LvtcQtHwSr Rf6lJA9Owe3+mlHcHYG2FGDTYe7QyRNcLGo8FJl+wzksispK8c8fQyTWHz7kpW1SKKHErD TXOVq23qAbY6yCP1ZIbIUQXMRk/V8yhVbWRLS/WBpx5V268wwsBNp3YsCEUphps6UV+Woo +5zWXHXKI/60yQc2Z2o+7UIvyU8P4klBbu2MWR3H5jEcXhaeOeQtc2CIROhNWA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1611563429; 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=fT0yLbgSHXoqxC+Ppvc+ZiBYpclK9xLccUp9T4OyAhY=; b=S2syWgU3yZgLg/oaHo2t20FatHzVXsIl9VXp9sdRxxBc0ky1BpeVBdetISF1tcmB303Ecv R6P97UX0GXtoGCDw== From: Sebastian Andrzej Siewior To: Christoph Hellwig Cc: Hannes Reinecke , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Jens Axboe , Thomas Gleixner , Peter Zijlstra , Ingo Molnar Subject: Re: [PATCH 2/3] blk-mq: Always complete remote completions requests in softirq Message-ID: <20210125083029.utnjqs2s3diqb5vx@linutronix.de> References: <20210123201027.3262800-1-bigeasy@linutronix.de> <20210123201027.3262800-3-bigeasy@linutronix.de> <30ce5ce2-8b9a-8873-4b37-c8720300942b@suse.de> <20210125082542.GC942655@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210125082542.GC942655@infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-01-25 08:25:42 [+0000], Christoph Hellwig wrote: > On Mon, Jan 25, 2021 at 08:10:16AM +0100, Hannes Reinecke wrote: > > I don't get this. > > This code is about _avoiding_ having to raise a softirq if the driver > > exports more than one hardware queue. > > So where exactly does the remote CPU case come in here? > > __blk_mq_complete_request_remote is only called for the case where we > do not completelky locally. The case that "degrades" here is where > the device supports multiple queues, but less than the number of CPUs, > and we bounce the completion to another CPU. Does it really "degrade" or just use the softirq more often? The usual case is run the softirqs in irq_exit() which is just after IPI. Sebastian