Re: IRQ_PIPELINE: TSC marked as unstable

[Philippe Gerum <rpm@xenomai.org>]

Philippe Gerum <rpm@xenomai.org> writes:

> Bezdeka, Florian <florian.bezdeka@siemens.com> writes:
>
>> Hi all,
>>
>> I'm able to reproduce the following on two different platforms now, so
>> I assume it's a IRQ_PIPELINE generic issue:
>>
>> Platform A):
>> Intel(R) Xeon(R) CPU D-1518 @ 2.20GHz
>> 1 Socket, 4 Cores, 1 thread per core
>>
>> Platform B):
>> Intel(R) Xeon(R) CPU E5-2620 0 @ 2.00GHz
>> 2 Sockets, 6 cores per socket, 2 threads per core
>> (2 NUMA nodes)
>>
>>
>> Platform A) reports the TSC being unstable during the boot phase,
>> platform B) reports the TSC as unstable when running stress tests:
>>
>> Taken from a B) based system:
>>
>> [57615.671114] clocksource: timekeeping watchdog on CPU17: Marking clocksource 'tsc' as unstable because the skew is too large:
>> [57615.738269] clocksource:                       'hpet' wd_now: 12f85ed0 wd_last: 2c5eab7b mask: ffffffff
>> [57615.794489] clocksource:                       'tsc' cs_now: 68e299c3708c cs_last: 6864c6ea3970 mask: ffffffffffffffff
>> [57615.858552] tsc: Marking TSC unstable due to clocksource watchdog
>> [57615.858582] TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.
>> [57615.910138] sched_clock: Marking unstable (57615104375773, 749891156)<-(57616072553488, -213973554)
>> [57615.905983] clocksource: Checking clocksource tsc synchronization from CPU 15.
>> [57615.949626] clocksource: Override clocksource tsc is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode
>> [57616.016343] clocksource: Switched to clocksource hpet
>>
>> The clocksource watchdog is migrated between CPUs to make sure the TSC
>> is synchronized between cores. For me it looks like a late delivery of
>> the watchdog timer.
>>
>> Available workaround(s):
>> - Add "tsc=reliable" to the kernel cmdline args
>> - At least for A) based systems it helped to apply the following diff to the kernel
>>   configuration. I do not consider that as "solution" for now.
>>
>> -CONFIG_HZ_100=y
>> +CONFIG_HZ_1000=y
>>
>>
>> As soon as I disable CONFIG_IRQ_PIPELINE the problem is gone.
>>
>> I already tried testing with CONFIG_DEBUG_IRQ_PIPELINE enabled, but
>> that didn't help so far.
>>
>> Any advise how to debug that?
>>
>> Best regards,
>> Florian
>
> Could this be related [1] (HPET stanza)?
>
> [1] https://evlproject.org/core/caveat/#x86-caveat


Not directly, you do have HPET enabled and the refined source is not
involved. Did you try enabling the Dovetail torture tests, particularly
on the machine that has the issue at boot time?

-- 
Philippe.