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| author | Thomas Gleixner <tglx@linutronix.de> | 2017-08-15 09:50:13 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2017-08-18 12:35:02 +0200 |
| commit | 7edaeb6841dfb27e362288ab8466ebdc4972e867 (patch) | |
| tree | 419ce3f71f7ffc17131bb911fb16ff037e3c6bb1 /lib/Kconfig.debug | |
| parent | ef954844c7ace62f773f4f23e28d2d915adc419f (diff) | |
| download | lwn-7edaeb6841dfb27e362288ab8466ebdc4972e867.tar.gz lwn-7edaeb6841dfb27e362288ab8466ebdc4972e867.zip | |
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/Kconfig.debug')
| -rw-r--r-- | lib/Kconfig.debug | 7 |
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. # |