[Intel-gfx] freedesktop bug id: 100548, bisected to sched/clock commit

[Martin Peres]

On 12/04/17 17:32, Peter Zijlstra wrote:
> On Wed, Apr 12, 2017 at 04:40:11PM +0300, Martin Peres wrote:
>
>>>> So, why is this only affecting the Core 2 Duo?
>>>
>>> Core2 doesn't have a usable TSC and would revert to the slow path. I'll
>>> have another look at that patch.
>>>
>>
>> So, by default, it is using the hpet clock source. FYI, I tried the only
>> other available clock source (acpi_pm) and got the same result.
>
> So because HPET is unbearably slow we've cobbled together something that
> takes the HPET (or rather get-time-of-day CLOCK_MONOTONIC) value at tick
> time and uses TSC to add per-cpu increments to that. Using windowing to
> keep the TSC maddness at bay.
>
> The patch in question affects the windowing.. clearly something went
> amiss.
>

Good to know. Is there a way to disable this behaviour, as a workaround 
for our CI system until a proper fix lands? We already pushed locally 
the revert for this patch, but that may affect other platforms which do 
not exhibit the problem.