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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 427A4C6FD1F for ; Wed, 22 Mar 2023 07:36:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229961AbjCVHgm (ORCPT ); Wed, 22 Mar 2023 03:36:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41430 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229939AbjCVHg2 (ORCPT ); Wed, 22 Mar 2023 03:36:28 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0C3475C9C4; Wed, 22 Mar 2023 00:36:25 -0700 (PDT) Received: from kwepemm600003.china.huawei.com (unknown [172.30.72.56]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4PhKvd3Gpbz17KpN; Wed, 22 Mar 2023 15:33:17 +0800 (CST) Received: from [10.67.111.205] (10.67.111.205) by kwepemm600003.china.huawei.com (7.193.23.202) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.21; Wed, 22 Mar 2023 15:36:23 +0800 Subject: Re: [PATCH RESEND v3] perf/core: Fix hardlockup failure caused by perf throttle From: Yang Jihong To: , , , , , , , , , , References: <20230227023508.102230-1-yangjihong1@huawei.com> <12782722-103e-88a9-df3e-6815b4734bc3@huawei.com> Message-ID: <37d019af-191c-9955-2417-b7cfa5e5efa3@huawei.com> Date: Wed, 22 Mar 2023 15:36:22 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <12782722-103e-88a9-df3e-6815b4734bc3@huawei.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.111.205] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To kwepemm600003.china.huawei.com (7.193.23.202) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, PING. This patch has not been responded. Please take time to check whether the fix solution is OK. Look forward to reviewing the patch. Thanks :) Thanks, Yang. On 2023/3/6 9:14, Yang Jihong wrote: > Hello, > > PING. > > Thanks, > Yang. > > On 2023/2/27 10:35, Yang Jihong wrote: >> commit e050e3f0a71bf ("perf: Fix broken interrupt rate throttling") >> introduces a change in throttling threshold judgment. Before this, >> compare hwc->interrupts and max_samples_per_tick, then increase >> hwc->interrupts by 1, but this commit reverses order of these two >> behaviors, causing the semantics of max_samples_per_tick to change. >> In literal sense of "max_samples_per_tick", if hwc->interrupts == >> max_samples_per_tick, it should not be throttled, therefore, the judgment >> condition should be changed to "hwc->interrupts > max_samples_per_tick". >> >> In fact, this may cause the hardlockup to fail, The minimum value of >> max_samples_per_tick may be 1, in this case, the return value of >> __perf_event_account_interrupt function is 1. >> As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86 >> architecture as an example, see x86_pmu_handle_irq). >> >> Fixes: e050e3f0a71b ("perf: Fix broken interrupt rate throttling") >> Signed-off-by: Yang Jihong >> --- >> >> Changes since v2: >>    - Add fixed commit. >> >> Changes since v1: >>    - Modify commit title. >> >>   kernel/events/core.c | 2 +- >>   1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/events/core.c b/kernel/events/core.c >> index f79fd8b87f75..0540a8653906 100644 >> --- a/kernel/events/core.c >> +++ b/kernel/events/core.c >> @@ -9434,7 +9434,7 @@ __perf_event_account_interrupt(struct perf_event >> *event, int throttle) >>       } else { >>           hwc->interrupts++; >>           if (unlikely(throttle >> -                 && hwc->interrupts >= max_samples_per_tick)) { >> +                 && hwc->interrupts > max_samples_per_tick)) { >>               __this_cpu_inc(perf_throttled_count); >>               tick_dep_set_cpu(smp_processor_id(), >> TICK_DEP_BIT_PERF_EVENTS); >>               hwc->interrupts = MAX_INTERRUPTS; >> > > .