[Intel-xe] [PATCH v2 2/2] drm/xe/pmu: Enable PMU interface

[Iddamsetty, Aravind]

On 06-07-2023 08:09, Dixit, Ashutosh wrote:
> On Tue, 27 Jun 2023 05:21:13 -0700, Aravind Iddamsetty wrote:
>>
> 
> Hi Aravind,
> 
Hi Ashutosh,
>> +static u64 __engine_group_busyness_read(struct xe_gt *gt, u64 config)
>> +{
>> +	u64 val = 0;
>> +
>> +	switch (config) {
>> +	case XE_PMU_RENDER_GROUP_BUSY(0):
>> +		val = xe_mmio_read32(gt, XE_OAG_RENDER_BUSY_FREE);
>> +		break;
>> +	case XE_PMU_COPY_GROUP_BUSY(0):
>> +		val = xe_mmio_read32(gt, XE_OAG_BLT_BUSY_FREE);
>> +		break;
>> +	case XE_PMU_MEDIA_GROUP_BUSY(0):
>> +		val = xe_mmio_read32(gt, XE_OAG_ANY_MEDIA_FF_BUSY_FREE);
>> +		break;
>> +	case XE_PMU_ANY_ENGINE_GROUP_BUSY(0):
>> +		val = xe_mmio_read32(gt, XE_OAG_RC0_ANY_ENGINE_BUSY_FREE);
>> +		break;
>> +	default:
>> +		drm_warn(&gt->tile->xe->drm, "unknown pmu event\n");
>> +	}
>> +
>> +	return xe_gt_clock_interval_to_ns(gt, val * 16);
>> +}
> 
> A few questions on just the above function first:
> 
> 1. OK so these registers won't be available to VF's, but any idea what
>    these counts are when VF's are active?

VF's cannot access the registers but the counters will be incrementing
if respective engines are busy and can be monitored from PF and that
will be across all VFs.

> 
> 2. When would these 32 bit registers overflow? Let us say a group is
>    continuously busy and we are running at 1 GHz, the registers would
>    overflow in 4 seconds (max value 4G)?

Based on BSPEC:52071 they use MHZ clock assuming the default 24MHz, it
would take around 5726 secs to overflow.

> 
> 3. What is the multiplication by 16 (not factored above in 2.)? I don't see
>    that in Bspec.

These counters are incremented based on crystal clock frequency and we
need to convert to CS time base hence a 16x mul. BSPEC:52071

Thanks,
Aravind.
> 
> Thanks.
> --
> Ashutosh