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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 EA104C433ED for ; Fri, 7 May 2021 07:30:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C104D613EA for ; Fri, 7 May 2021 07:30:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233883AbhEGHbN (ORCPT ); Fri, 7 May 2021 03:31:13 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:17592 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232268AbhEGHbL (ORCPT ); Fri, 7 May 2021 03:31:11 -0400 Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4Fc28k5WWvz1BJpP; Fri, 7 May 2021 15:27:34 +0800 (CST) Received: from [10.67.110.136] (10.67.110.136) by DGGEMS402-HUB.china.huawei.com (10.3.19.202) with Microsoft SMTP Server id 14.3.498.0; Fri, 7 May 2021 15:30:06 +0800 Subject: Re: [PATCH v3 03/16] arm64: Allow IPIs to be handled as normal interrupts To: Marc Zyngier CC: , , , , , , , , , , , , , , References: <87pmy4qe7e.wl-maz@kernel.org> From: He Ying Message-ID: Date: Fri, 7 May 2021 15:30:06 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <87pmy4qe7e.wl-maz@kernel.org> Content-Type: text/plain; charset="gbk"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.110.136] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ÔÚ 2021/5/6 19:44, Marc Zyngier дµÀ: > 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? OK. We have just calculated the pmu cycles from the entry of gic_handle_irq to the entry of do_handle_ipi. Here is some more information about our test: CPU: Hisilicon hip05-d02 Applying the patch series: 1115 cycles Reverting the patch series: 599 cycles > >> 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? I'm afraid not. We just run some benchmarks and calculated pmu cycle counters. But we have observed running time from the entry of gic_handle_irq to the entry of do_handle_ipi almost doubles. Doesn't it affect 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. OK. > >> 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). OK. I see the patch series. Would it be applied to the mainline someday? I notice that more than 5 months have passed since you sent the patch series. Thanks. > > Thanks, > > M. > > [1] https://lore.kernel.org/lkml/20201124141449.572446-1-maz@kernel.org/ >