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=-9.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 C9C18C4363A for ; Tue, 27 Oct 2020 10:38:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 660A020829 for ; Tue, 27 Oct 2020 10:38:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603795083; bh=OcnUMuBA901Kxhgnt8GvlIDOQoOTk8b7CBTnQqnMdA8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=bHeY+JC8jU65dtRmaj2TpJuAw+EgFffhn4LMvXjRoSsVicWMfifDMnlGvPNW9udvO gChO9MQfAS/2JlrSbwFSZ06qUwEA0zcD/dd5JyX9bAGQJLiZmLKSmWhjmlbIq3lG5y w9C/oYay7xTDNe8NCW1+7c3Us9Xn8pV1WhnozuYQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2898497AbgJ0KiB (ORCPT ); Tue, 27 Oct 2020 06:38:01 -0400 Received: from mail.kernel.org ([198.145.29.99]:60826 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2436614AbgJ0Khj (ORCPT ); Tue, 27 Oct 2020 06:37:39 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EEEE220780; Tue, 27 Oct 2020 10:37:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603795058; bh=OcnUMuBA901Kxhgnt8GvlIDOQoOTk8b7CBTnQqnMdA8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ByIyJYnP5TAv58na/z32RMBoNQLgO1yRlAqQcGR9525dLfUziBthSg+Co5jEVdMD2 W4tzYJ+b8d3ayNdzu0R7d1OrhEwgPKGE7uCPJgAtB9oaUaJXkaOML43XwzJ4zO/8sR WiLVnMc3T66iXivOM/IoLHBB7+/CBhI6jpHtxJoo= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1kXMMB-004eav-WC; Tue, 27 Oct 2020 10:37:36 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 27 Oct 2020 10:37:35 +0000 From: Marc Zyngier To: Vincent Guittot Cc: LAK , linux-kernel , Will Deacon , Catalin Marinas , Russell King , Thomas Gleixner , Jason Cooper , Sumit Garg , Valentin Schneider , Florian Fainelli , Gregory Clement , Andrew Lunn , Saravana Kannan , Android Kernel Team Subject: Re: [PATCH v3 03/16] arm64: Allow IPIs to be handled as normal interrupts In-Reply-To: References: <20200901144324.1071694-1-maz@kernel.org> <20200901144324.1071694-4-maz@kernel.org> <353f13b0dcc6c7ea1b44012d9632a0cc@kernel.org> User-Agent: Roundcube Webmail/1.4.9 Message-ID: <7b754dfe579044902d3468b9f864bd37@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: vincent.guittot@linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, linux@arm.linux.org.uk, tglx@linutronix.de, jason@lakedaemon.net, sumit.garg@linaro.org, Valentin.Schneider@arm.com, f.fainelli@gmail.com, gregory.clement@bootlin.com, andrew@lunn.ch, saravanak@google.com, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-10-27 10:12, Vincent Guittot wrote: > HI Marc, > > On Mon, 19 Oct 2020 at 17:43, Vincent Guittot > wrote: >> >> On Mon, 19 Oct 2020 at 15:04, Marc Zyngier wrote: >> > > > ... > >> > >> >> > >> One of the major difference is that we end up, in some cases >> > >> (such as when performing IRQ time accounting on the scheduler >> > >> IPI), end up with nested irq_enter()/irq_exit() pairs. >> > >> Other than the (relatively small) overhead, there should be >> > >> no consequences to it (these pairs are designed to nest >> > >> correctly, and the accounting shouldn't be off). >> > > >> > > While rebasing on mainline, I have faced a performance regression for >> > > the benchmark: >> > > perf bench sched pipe >> > > on my arm64 dual quad core (hikey) and my 2 nodes x 112 CPUS (thx2) >> > > >> > > The regression comes from: >> > > commit: d3afc7f12987 ("arm64: Allow IPIs to be handled as normal >> > > interrupts") >> > >> > That's interesting, as this patch doesn't really change anything (most >> > of the potential overhead comes in later). The only potential overhead >> > I can see is that the scheduler_ipi() call is now wrapped around >> > irq_enter()/irq_exit(). >> > >> > > >> > > v5.9 + this patch >> > > hikey : 48818(+/- 0.31) 37503(+/- 0.15%) -23.2% >> > > thx2 : 132410(+/- 1.72) 122646(+/- 1.92%) -7.4% >> > > >> > > By + this patch, I mean merging branch from this patch. Whereas >> > > merging the previous: >> > > commit: 83cfac95c018 ("genirq: Allow interrupts to be excluded from >> > > /proc/interrupts") >> > > It doesn't show any regression >> > >> > Since you are running perf, can you spot where the overhead occurs? > > Any idea about the root cause of the regression ? > I have faced it on more arm64 platforms in the meantime two possible causes: (1) irq_enter/exit on the rescheduling IPI means we reschedule much more often (2) irq_domain lookups add some overhead. For (1), I have this series[1] which is ugly as sin and needs much more testing. For (2), I have some ideas which need more work (let the irq domain resolve to an irq_desc instead of an interrupt number, avoiding another radix-tree lookup). M. [1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=irq/ipi-fixes -- Jazz is not dead. It just smells funny...