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 8A13CC433FE for ; Fri, 4 Nov 2022 01:02:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229700AbiKDBCt (ORCPT ); Thu, 3 Nov 2022 21:02:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53514 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229492AbiKDBCp (ORCPT ); Thu, 3 Nov 2022 21:02:45 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CAB8B1DDCA for ; Thu, 3 Nov 2022 18:01:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1667523711; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=29kSNJ5Ci7JoDk/A0Vviw2ALuH5OuGuOU8X9ZrGjDu0=; b=Ux8y/TYy9lmvwfGoo6OSMFtDa2H0FdfEJLi84U5J3LTJ9+GnpLPtNqF9wQNvgziSFwYNYh Cm4v1givqB+WPuEeJ3GXQj7trWua1kQW10Dzcog40GS1i7+8rjgNCmG7zieGrlG6GUe489 r7+7M61NvKLllsmBOXqJQkUt+bzlFQ0= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-624-KL5vKcO3MN6Gvle_URVBTQ-1; Thu, 03 Nov 2022 21:01:47 -0400 X-MC-Unique: KL5vKcO3MN6Gvle_URVBTQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D20583C0DDA5; Fri, 4 Nov 2022 01:01:46 +0000 (UTC) Received: from [10.22.33.38] (unknown [10.22.33.38]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0F1502166B26; Fri, 4 Nov 2022 01:01:46 +0000 (UTC) Message-ID: Date: Thu, 3 Nov 2022 21:01:45 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.0 Subject: Re: [PATCH clocksource 2/2] clocksource: Exponential backoff for load-induced bogus watchdog reads Content-Language: en-US To: paulmck@kernel.org Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, john.stultz@linaro.org, sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com, maz@kernel.org, kernel-team@meta.com, neeraju@codeaurora.org, ak@linux.intel.com, feng.tang@intel.com, zhengjun.xing@intel.com, John Stultz References: <20221102184001.GA1306489@paulmck-ThinkPad-P17-Gen-1> <20221102184009.1306751-2-paulmck@kernel.org> <1fdbdf78-cdca-975f-7f57-e391263d0aec@redhat.com> <20221103204910.GF5600@paulmck-ThinkPad-P17-Gen-1> <61470eb8-fc3c-7f95-881e-03da1805b5ac@redhat.com> <20221104002616.GH5600@paulmck-ThinkPad-P17-Gen-1> From: Waiman Long In-Reply-To: <20221104002616.GH5600@paulmck-ThinkPad-P17-Gen-1> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/3/22 20:26, Paul E. McKenney wrote: > On Thu, Nov 03, 2022 at 08:20:27PM -0400, Waiman Long wrote: >> On 11/3/22 16:49, Paul E. McKenney wrote: >>> commit da44b8af99222ff8761a98ca8c00837a7d607d28 >>> Author: Paul E. McKenney >>> Date: Fri Oct 28 10:38:58 2022 -0700 >>> >>> clocksource: Exponential backoff for load-induced bogus watchdog reads >>> The clocksource watchdog will reject measurements that are excessively >>> delayed, that is, by more than 1.5 seconds beyond the intended 0.5-second >>> watchdog interval. On an extremely busy system, this can result in a >>> console message being printed every two seconds. This is excessively >>> noisy for a non-error condition. >>> Therefore, apply exponential backoff to these messages. This exponential >>> backoff is capped at 1024 times the watchdog interval, which comes to >>> not quite one message per ten minutes. >>> Please note that the bogus watchdog reads that occur when the watchdog >>> interval is less than 0.125 seconds are still printed unconditionally >>> because these likely correspond to a serious error condition in the >>> timer code or hardware. >>> [ paulmck: Apply Feng Tang feedback. ] >>> [ paulmck: Apply Waiman Long feedback. ] >>> Reported-by: Waiman Long >>> Reported-by: Feng Tang >>> Signed-off-by: Paul E. McKenney >>> Cc: John Stultz >>> Cc: Thomas Gleixner >>> Cc: Stephen Boyd >>> Cc: Feng Tang >>> Cc: Waiman Long >>> >>> diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h >>> index 1d42d4b173271..23b73f2293d6d 100644 >>> --- a/include/linux/clocksource.h >>> +++ b/include/linux/clocksource.h >>> @@ -125,6 +125,9 @@ struct clocksource { >>> struct list_head wd_list; >>> u64 cs_last; >>> u64 wd_last; >>> + u64 wd_last_bogus; >>> + int wd_bogus_shift; >>> + unsigned long wd_bogus_count; >>> #endif >>> struct module *owner; >>> }; >>> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c >>> index 3f5317faf891f..1eefb56505350 100644 >>> --- a/kernel/time/clocksource.c >>> +++ b/kernel/time/clocksource.c >>> @@ -442,14 +442,33 @@ static void clocksource_watchdog(struct timer_list *unused) >>> /* Check for bogus measurements. */ >>> wdi = jiffies_to_nsecs(WATCHDOG_INTERVAL); >>> - if (wd_nsec < (wdi >> 2)) { >>> - /* This usually indicates broken timer code or hardware. */ >>> - pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced only %lld ns during %d-jiffy time interval, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL); >>> + if (wd_nsec > (wdi << 2) || cs_nsec > (wdi << 2)) { >>> + bool needwarn = false; >>> + u64 wd_lb; >>> + >>> + cs->wd_bogus_count++; >>> + if (!cs->wd_bogus_shift) { >>> + needwarn = true; >>> + } else { >>> + delta = clocksource_delta(wdnow, cs->wd_last_bogus, watchdog->mask); >>> + wd_lb = clocksource_cyc2ns(delta, watchdog->mult, watchdog->shift); >>> + if ((1 << cs->wd_bogus_shift) * wdi <= wd_lb) >>> + needwarn = true; >>> + } >>> + if (needwarn) { >>> + /* This can happen on busy systems, which can delay the watchdog. */ >>> + pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced an excessive %lld ns during %d-jiffy time interval (%lu additional), probable CPU overutilization, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL, cs->wd_bogus_count); >> Just one question, does "%lu additional" means the number of bogus count >> that doesn't meet the needwarn requirement and hence skipped. If so, I think >> you have to use "cs->wd_bogus_cnt - 1". Other than that, the change looks >> good to me. > It means the number since the last report, or, for the first report, > the number since boot. > > Does that work for you? OK, I think the word "additional" tricks me into thinking about extra bogus messages in additional to the current one. Using another word like "total" may be less confusing. Cheers, Longman