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McKenney" To: tglx@linutronix.de Cc: 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, "Paul E. McKenney" , Waiman Long , John Stultz Subject: [PATCH clocksource 2/2] clocksource: Exponential backoff for load-induced bogus watchdog reads Date: Wed, 2 Nov 2022 11:40:09 -0700 Message-Id: <20221102184009.1306751-2-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20221102184001.GA1306489@paulmck-ThinkPad-P17-Gen-1> References: <20221102184001.GA1306489@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 X-Spam-Status: No, score=-8.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1748410834059213080?= X-GMAIL-MSGID: =?utf-8?q?1748410834059213080?= 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. ] 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 Reviewed-by: Feng Tang Reviewed-by: Waiman Long --- include/linux/clocksource.h | 4 ++++ kernel/time/clocksource.c | 31 +++++++++++++++++++++++++------ 2 files changed, 29 insertions(+), 6 deletions(-) diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index 1d42d4b173271..daac05aedf56a 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -125,6 +125,10 @@ 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; + unsigned long wd_bogus_count_last; #endif struct module *owner; }; diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 3f5317faf891f..de8047b6720f5 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 - cs->wd_bogus_count_last); + cs->wd_last_bogus = wdnow; + if (cs->wd_bogus_shift < 10) + cs->wd_bogus_shift++; + cs->wd_bogus_count_last = cs->wd_bogus_count; + } continue; } - if (wd_nsec > (wdi << 2)) { - /* 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, probable CPU overutilization, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL); + /* Check too-short measurements second to handle wrap. */ + if (wd_nsec < (wdi >> 2) || cs_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); continue; }