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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 2/3] clocksource: Add comments to classify bogus measurements Date: Mon, 14 Nov 2022 15:28:25 -0800 Message-Id: <20221114232827.835599-2-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20221114232807.GA834337@paulmck-ThinkPad-P17-Gen-1> References: <20221114232807.GA834337@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 X-Spam-Status: No, score=-7.1 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?1749516936138436145?= X-GMAIL-MSGID: =?utf-8?q?1749516936138436145?= An extremely busy system can delay the clocksource watchdog, so that the corresponding too-long bogus-measurement error does not necessarily imply an error in the system. However, a too-short bogus-measurement error likely indicates a bug in hardware, firmware or software. Therefore, add comments clarifying these bogus-measurement pr_warn()s. Reported-by: Feng Tang Signed-off-by: Paul E. McKenney Reviewed-by: Waiman Long Reviewed-by: Feng Tang Cc: John Stultz Cc: Thomas Gleixner Cc: Stephen Boyd --- kernel/time/clocksource.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index dcaf38c062161..3f5317faf891f 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -443,10 +443,12 @@ 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); 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); continue; }