From: Andi Kleen <ak@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Kan Liang <kan.liang@intel.com>,
linux-kernel@vger.kernel.org, dzickus@redhat.com,
mingo@kernel.org, akpm@linux-foundation.org,
babu.moger@oracle.com, atomlin@redhat.com, prarit@redhat.com,
torvalds@linux-foundation.org, peterz@infradead.org,
eranian@google.com, acme@redhat.com, stable@vger.kernel.org
Subject: Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups
Date: Wed, 21 Jun 2017 10:07:34 -0700 [thread overview]
Message-ID: <20170621170734.GF23705@tassilo.jf.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1706211645340.2328@nanos>
On Wed, Jun 21, 2017 at 05:12:06PM +0200, Thomas Gleixner wrote:
> On Wed, 21 Jun 2017, kan.liang@intel.com wrote:
> >
> > #ifdef CONFIG_HARDLOCKUP_DETECTOR
> > +/*
> > + * The NMI watchdog relies on PERF_COUNT_HW_CPU_CYCLES event, which
> > + * can tick faster than the measured CPU Frequency due to Turbo mode.
> > + * That can lead to spurious timeouts.
> > + * To workaround the issue, extending the period by 3 times.
> > + */
> > u64 hw_nmi_get_sample_period(int watchdog_thresh)
> > {
> > - return (u64)(cpu_khz) * 1000 * watchdog_thresh;
> > + return (u64)(cpu_khz) * 1000 * watchdog_thresh * 3;
>
> The maximum turbo frequency of any given machine can be retrieved.
Not reliably, e.g. not in virtualization. Also it would require
model specific checks, so as soon as you have a new model and an
old kernel it could still randomly fail.
-Andi
next prev parent reply other threads:[~2017-06-21 17:07 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-21 14:41 [PATCH V2] kernel/watchdog: fix spurious hard lockups kan.liang
2017-06-21 15:12 ` Thomas Gleixner
2017-06-21 15:47 ` Liang, Kan
2017-06-21 17:40 ` Prarit Bhargava
2017-06-21 17:07 ` Andi Kleen [this message]
2017-06-21 19:59 ` Thomas Gleixner
2017-06-21 21:53 ` Thomas Gleixner
2017-06-22 15:33 ` Thomas Gleixner
2017-06-22 15:44 ` Don Zickus
2017-06-22 15:48 ` Liang, Kan
2017-06-23 8:01 ` Thomas Gleixner
2017-06-23 16:29 ` Don Zickus
2017-06-23 21:50 ` Thomas Gleixner
2017-06-26 20:19 ` Don Zickus
2017-06-26 20:30 ` Thomas Gleixner
2017-06-27 20:12 ` Don Zickus
2017-06-27 20:49 ` Liang, Kan
2017-06-27 21:09 ` Don Zickus
2017-06-27 23:48 ` Andi Kleen
2017-06-28 19:00 ` Don Zickus
2017-06-28 20:14 ` Andi Kleen
2017-06-29 15:44 ` Don Zickus
2017-06-29 16:12 ` Andi Kleen
2017-06-29 16:26 ` Don Zickus
2017-06-29 16:36 ` Andi Kleen
2017-07-17 1:24 ` Liang, Kan
2017-07-17 7:14 ` Thomas Gleixner
2017-07-17 12:18 ` Liang, Kan
2017-07-17 13:13 ` Thomas Gleixner
2017-07-17 14:46 ` Liang, Kan
2017-07-17 15:00 ` Thomas Gleixner
2017-07-17 14:46 ` Don Zickus
2017-08-15 1:16 ` Liang, Kan
2017-08-15 1:28 ` Linus Torvalds
2017-08-15 7:50 ` Thomas Gleixner
2017-08-17 15:45 ` Liang, Kan
2017-08-18 10:39 ` [tip:core/urgent] kernel/watchdog: Prevent false positives with turbo modes tip-bot for Thomas Gleixner
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