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 893E9C77B70 for ; Fri, 14 Apr 2023 07:04:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229547AbjDNHET (ORCPT ); Fri, 14 Apr 2023 03:04:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42552 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229663AbjDNHER (ORCPT ); Fri, 14 Apr 2023 03:04:17 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6BF93A84; Fri, 14 Apr 2023 00:04:15 -0700 (PDT) Received: from kwepemm600003.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4PyS6R54MLzKxvD; Fri, 14 Apr 2023 15:01:35 +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 15.1.2507.23; Fri, 14 Apr 2023 15:04:11 +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> <37d019af-191c-9955-2417-b7cfa5e5efa3@huawei.com> Message-ID: <56cc5b4f-3cbd-c265-36fc-fedab16b8cff@huawei.com> Date: Fri, 14 Apr 2023 15:04:11 +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: <37d019af-191c-9955-2417-b7cfa5e5efa3@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: dggems702-chm.china.huawei.com (10.3.19.179) To kwepemm600003.china.huawei.com (7.193.23.202) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org Hello, PING again. Look forward the review. Thanks, Yang. On 2023/3/22 15:36, Yang Jihong wrote: > 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; >>> >> >> . > > .