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 44964C55178 for ; Tue, 27 Oct 2020 17:59:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E2AF421556 for ; Tue, 27 Oct 2020 17:59:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="npuz5bBu"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="LcxebdN0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1823662AbgJ0R70 (ORCPT ); Tue, 27 Oct 2020 13:59:26 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:48178 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1823648AbgJ0R7Y (ORCPT ); Tue, 27 Oct 2020 13:59:24 -0400 Date: Tue, 27 Oct 2020 18:59:20 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1603821563; 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=2YW3/NPOF7xoOmIn/XQxXTt+kGRGSQ42qcp9fBVrIJk=; b=npuz5bBuIFtgaJkz2yZDJqvqxLRL2LxwJj1bT1HOHH9zo+BtG80cW47qVn/vciZrJ5p7Qq 1RegbSGjpMqqrID6s5D7zPyPsOyf62iW2VLvZuun0QqxkOM5MtKLZ3+ICo/G5TEj7RhcHF tLVSo7VYjbFq6Y2ZTnzTzLJRSkLANVe9mGA/it/7pevqf2shFJgqWOspI37lEifmB19rKv 4Bs3el3Vpjv8H/2Lek6zdP+Il16Fbj6QjnKVqVe+85HiahOH5i6SGJtypiia/ZgG5WFFY+ ZpZCzLUnfNEyvffDKZeEtsGNg3/bB7hRc5wjPUoQGwEvc6EWIgkOVbUANNIbrA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1603821563; 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=2YW3/NPOF7xoOmIn/XQxXTt+kGRGSQ42qcp9fBVrIJk=; b=LcxebdN0zE4/+u9RlIK5b3xel6TFXwAj09aw3buCO7iKRwRoG1f55H2rxIBaXqNyaPtgDB P1/Jy31B2lRgt/Dw== From: Sebastian Andrzej Siewior To: Christoph Hellwig Cc: Thomas Gleixner , David Runge , linux-rt-users@vger.kernel.org, Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Daniel Wagner Subject: Re: [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT Message-ID: <20201027175920.otcm2ox7vxce5k3c@linutronix.de> References: <20201021175059.GA4989@hmbx> <20201023110400.bx3uzsb7xy5jtsea@linutronix.de> <20201023112130.GA23790@infradead.org> <20201023135219.mzzl76eqqy6tqwhe@linutronix.de> <20201027092606.GA20805@infradead.org> <20201027101102.cvczdb3mkvtoguo5@linutronix.de> <20201027160742.GA19073@infradead.org> <87eelj1tx0.fsf@nanos.tec.linutronix.de> <20201027172309.GA15004@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201027172309.GA15004@infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On 2020-10-27 17:23:09 [+0000], Christoph Hellwig wrote: > On Tue, Oct 27, 2020 at 06:05:15PM +0100, Thomas Gleixner wrote: > > > Is there a way to raise a softirq and preferably place it on a given > > > CPU without our IPI dance? That should be a win-win situation for > > > everyone. > > > > Not really. Softirq pending bits are strictly per cpu and we don't have > > locking or atomics to set them remotely. Even if we had that, then you'd > > still need a mechanism to make sure that the remote CPU actually > > processes them. So you'd still need an IPI of some sorts. > > Ok. I was hoping we could hide this in core code somehow, especially > a peterz didn't like the use of smp_call_function_single_async in the > blk-mq completion code very much. > > Sebastian, would this solve your preempt-rt and lockdep issues? second. I'm cooking something. Sebastian