Re: [PATCH igt] igt/perf_pmu: Recalibrate interrupt loop.

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 24/11/2017 09:28, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2017-11-24 09:11:06)
>>
>> On 23/11/2017 15:03, Chris Wilson wrote:
>>> We have to be careful in our calibration loop, too slow and we timeout,
>>> too fast and we don't emit an interrupt! On fast legacy devices, we
>>> would overflow the calibration calcuation...
>>>
>>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>>> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>> ---
>>> -     sz = ALIGN(sz, sizeof(uint32_t));
>>> +     sz = calibrate_nop(gem_fd, 1e6 / target);
>>> +     gem_quiescent_gpu(gem_fd);
>>> +
>>> +     fd = open_pmu(I915_PMU_INTERRUPTS);
>>> +     spin = igt_spin_batch_new(gem_fd, 0, 0, 0);
>>
>> What's the spin batch for?
> 
> It's just a plug to ensure that the queue of calibrated execs don't start
> executing before we're waiting on them. Instead of doing exec + sync, we
> want to switch to exec[N] + sync.

Of course, makes sense.

Only improvement I can think of is to define the target time (1e6) and 
poll timeout (2000ms) from a common local variable.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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