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authorThomas Gleixner <tglx@linutronix.de>2017-08-15 09:50:13 +0200
committerThomas Gleixner <tglx@linutronix.de>2017-08-18 12:35:02 +0200
commit7edaeb6841dfb27e362288ab8466ebdc4972e867 (patch)
tree419ce3f71f7ffc17131bb911fb16ff037e3c6bb1 /lib
parentef954844c7ace62f773f4f23e28d2d915adc419f (diff)
downloadlinux-next-7edaeb6841dfb27e362288ab8466ebdc4972e867.tar.gz
kernel/watchdog: Prevent false positives with turbo modes
The hardlockup detector on x86 uses a performance counter based on unhalted CPU cycles and a periodic hrtimer. The hrtimer period is about 2/5 of the performance counter period, so the hrtimer should fire 2-3 times before the performance counter NMI fires. The NMI code checks whether the hrtimer fired since the last invocation. If not, it assumess a hard lockup. The calculation of those periods is based on the nominal CPU frequency. Turbo modes increase the CPU clock frequency and therefore shorten the period of the perf/NMI watchdog. With extreme Turbo-modes (3x nominal frequency) the perf/NMI period is shorter than the hrtimer period which leads to false positives. A simple fix would be to shorten the hrtimer period, but that comes with the side effect of more frequent hrtimer and softlockup thread wakeups, which is not desired. Implement a low pass filter, which checks the perf/NMI period against kernel time. If the perf/NMI fires before 4/5 of the watchdog period has elapsed then the event is ignored and postponed to the next perf/NMI. That solves the problem and avoids the overhead of shorter hrtimer periods and more frequent softlockup thread wakeups. Fixes: 58687acba592 ("lockup_detector: Combine nmi_watchdog and softlockup detector") Reported-and-tested-by: Kan Liang <Kan.liang@intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: dzickus@redhat.com Cc: prarit@redhat.com Cc: ak@linux.intel.com Cc: babu.moger@oracle.com Cc: peterz@infradead.org Cc: eranian@google.com Cc: acme@redhat.com Cc: stable@vger.kernel.org Cc: atomlin@redhat.com Cc: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1708150931310.1886@nanos
Diffstat (limited to 'lib')
-rw-r--r--lib/Kconfig.debug7
1 files changed, 7 insertions, 0 deletions
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 98fe715522e8..c617b9d1d6cb 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -798,6 +798,13 @@ config HARDLOCKUP_DETECTOR_PERF
select SOFTLOCKUP_DETECTOR
#
+# Enables a timestamp based low pass filter to compensate for perf based
+# hard lockup detection which runs too fast due to turbo modes.
+#
+config HARDLOCKUP_CHECK_TIMESTAMP
+ bool
+
+#
# arch/ can define HAVE_HARDLOCKUP_DETECTOR_ARCH to provide their own hard
# lockup detector rather than the perf based detector.
#