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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 88457C433E1 for ; Thu, 20 Aug 2020 13:08:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 61BBC207BB for ; Thu, 20 Aug 2020 13:08:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="P8x86hz0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730006AbgHTNIh (ORCPT ); Thu, 20 Aug 2020 09:08:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34424 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728848AbgHTNIc (ORCPT ); Thu, 20 Aug 2020 09:08:32 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 358D1C061385 for ; Thu, 20 Aug 2020 06:08:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=E3zojqPhdk7VSZAujguQkn+IVWrkry8akdjcjCF1GMY=; b=P8x86hz0Jfe9ms3orxSszObeD+ ypy4aFu7xOCkhBcWo5N9X2PZAeROH+GK/+MdXh9NR9rGxoFBETN4/d8RZcVBZ8rOLd3OAV2zQKdtT uCCbZ16bpdOJFjYq6dww6ynDe4tzVX7z/2AzDqiVFLbHE3GPTVoey/faxfrBQp36uHmg6DQ3BXhwL uY9LAxIoSB0ptToc+Csmgh/E6ZbzvrhXNlUvY6WTR1c97mJRvfTC3tv6FtOq+SH8fqT6HGwbkeYsG doMHDJ/5oVxwRtE3wu8YFlb2QE8ooVWcmtPo+L60Ge96U+LMDExnyPHKIkgOc47SX6JuuKoVFUegK zx01TIRQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1k8kIi-0000zQ-Pp; Thu, 20 Aug 2020 13:08:17 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 8D75B305E21; Thu, 20 Aug 2020 15:08:12 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 417CD28B7E840; Thu, 20 Aug 2020 15:08:12 +0200 (CEST) Date: Thu, 20 Aug 2020 15:08:12 +0200 From: peterz@infradead.org To: Linus Torvalds Cc: Christoph Hellwig , Ingo Molnar , Linux Kernel Mailing List , Will Deacon , "Paul E. McKenney" , Jens Axboe , Chris Wilson , David Miller , Jakub Kicinski , =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , Oleg Nesterov , Vincent Guittot Subject: Re: [RFC][PATCH v2 08/10] smp,irq_work: Use the new irq_work API Message-ID: <20200820130812.GU2674@hirez.programming.kicks-ass.net> References: <20200818105102.926463950@infradead.org> <20200818112418.460474861@infradead.org> <20200818162542.GB27196@lst.de> <20200819072209.GU2674@hirez.programming.kicks-ass.net> <20200819194116.GJ2674@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 19, 2020 at 03:04:56PM -0700, Linus Torvalds wrote: > On Wed, Aug 19, 2020 at 12:41 PM wrote: > > > > I'm not sure I get the "expensive irq_work queues" argument, I fully > > agree with you that adding the atomic op is fairly crap. > > There's an atomic op on the actual runing side too, because of the > whole IRQ_WORK_PENDING thing. > > So you get that double hit. > > Maybe it doesn't matter. I just remember us being very careful to > avoid any unnecessary atomics in the smp_call_function area, but > admittedly I haven't worked on that code for a few years, so .. Patch #3 trades that atomic for a full barrier. Not a massive win on x86, but still.