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=-4.0 required=3.0 tests=BAYES_00,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 ADC4BC433ED for ; Thu, 6 May 2021 11:44:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6ECBC613D9 for ; Thu, 6 May 2021 11:44:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230349AbhEFLpl (ORCPT ); Thu, 6 May 2021 07:45:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:42014 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229777AbhEFLpk (ORCPT ); Thu, 6 May 2021 07:45:40 -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 29924610FC; Thu, 6 May 2021 11:44:42 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1lecQp-00BEVI-VJ; Thu, 06 May 2021 12:44:40 +0100 Date: Thu, 06 May 2021 12:44:21 +0100 Message-ID: <87pmy4qe7e.wl-maz@kernel.org> From: Marc Zyngier To: He Ying Cc: , , , , , , , , , , , , , , Subject: Re: [PATCH v3 03/16] arm64: Allow IPIs to be handled as normal interrupts In-Reply-To: References: User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: heying24@huawei.com, vincent.guittot@linaro.org, Valentin.Schneider@arm.com, andrew@lunn.ch, catalin.marinas@arm.com, f.fainelli@gmail.com, gregory.clement@bootlin.com, jason@lakedaemon.net, kernel-team@android.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux@arm.linux.org.uk, saravanak@google.com, sumit.garg@linaro.org, tglx@linutronix.de, will@kernel.org 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 Thu, 06 May 2021 08:50:42 +0100, He Ying wrote: > > Hello Marc, > > We have faced a performance regression for handling ipis since this > commit. I think it's the same issue reported by Vincent. Can you share more details on what regression you have observed? What's the workload, the system, the performance drop? > I found you pointed out the possible two causes: > > (1) irq_enter/exit on the rescheduling IPI means we reschedule much > more often. It turned out to be a red herring. We don't reschedule more often, but we instead suffer from the overhead of irq_enter()/irq_exit(). However, this only matters for silly benchmarks, and no real-life workload showed any significant regression. Have you identified such realistic workload? > (2) irq_domain lookups add some overhead. While this is also a potential source of overhead, it turned out not to be the case. > But I don't see any following patches in mainline. So, are you still > working on this issue? Looking forward to your reply. See [1]. However, there is probably better things to do than this low-level specialisation of IPIs, and Thomas outlined what needs to be done (see v1 of the patch series). Thanks, M. [1] https://lore.kernel.org/lkml/20201124141449.572446-1-maz@kernel.org/ -- Without deviation from the norm, progress is not possible.