From: "Liang, Kan" <kan.liang@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"dzickus@redhat.com" <dzickus@redhat.com>,
"mingo@kernel.org" <mingo@kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"babu.moger@oracle.com" <babu.moger@oracle.com>,
"atomlin@redhat.com" <atomlin@redhat.com>,
"prarit@redhat.com" <prarit@redhat.com>,
"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
"peterz@infradead.org" <peterz@infradead.org>,
"eranian@google.com" <eranian@google.com>,
"acme@redhat.com" <acme@redhat.com>,
"ak@linux.intel.com" <ak@linux.intel.com>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH V2] kernel/watchdog: fix spurious hard lockups
Date: Wed, 21 Jun 2017 15:47:13 +0000 [thread overview]
Message-ID: <37D7C6CF3E00A74B8858931C1DB2F077537101A3@SHSMSX103.ccr.corp.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1706211645340.2328@nanos>
> 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.
The maximum turbo frequency is determined by the model of processor.
I'm not sure if there is a generic way to get the maximum turbo frequency.
Is there?
Thanks,
Kan
>
> So why don't you simply take that ratio into account and apply it for the
> machines which have those insane turbo loaders? That's not a huge effort,
> can be easily backported and does not inflict this unconditially.
>
> So what you want is:
>
> return get_max_turbo_khz() * 1000 * watchdog_thresh;
>
> Where get_max_turbo_khz() by default returns cpu_khz for non turbo
> motors.
>
> And instead of silently doing this it should emit a info into dmesg:
>
> u64 period, max_khz = get_max_turbo_khz();
> static int once;
>
> period = max_khz * 1000 * watchdog_thresh;
>
> if (max_khz != cpu_khz && !once) {
> unsigned int msec = period / cpu_khz;
>
> once = 1;
> pr_info("Adjusted watchdog threshold to %u.%04u sec\n",
> msec / 1000, msec % 1000);
> }
>
> return period;
>
> Hmm?
>
> Thanks,
>
> tglx
next prev parent reply other threads:[~2017-06-21 17:09 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 [this message]
2017-06-21 17:40 ` Prarit Bhargava
2017-06-21 17:07 ` Andi Kleen
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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