[PATCH] drm/amdgpu: change read of GPU clock counter on Vega10 VF

[Kuehling, Felix]

On 2019-11-05 5:03 p.m., Huang, JinHuiEric wrote:
> Using unified VBIOS has performance drop in sriov environment.
> The fix is switching to another register instead.
>
> Signed-off-by: Eric Huang <JinhuiEric.Huang at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c | 18 +++++++++++++++---
>   1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> index 829d623..6770bd1 100644
> --- a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> @@ -3885,9 +3885,21 @@ static uint64_t gfx_v9_0_get_gpu_clock_counter(struct amdgpu_device *adev)
>   	uint64_t clock;
>   
>   	mutex_lock(&adev->gfx.gpu_clock_mutex);
> -	WREG32_SOC15(GC, 0, mmRLC_CAPTURE_GPU_CLOCK_COUNT, 1);
> -	clock = (uint64_t)RREG32_SOC15(GC, 0, mmRLC_GPU_CLOCK_COUNT_LSB) |
> -		((uint64_t)RREG32_SOC15(GC, 0, mmRLC_GPU_CLOCK_COUNT_MSB) << 32ULL);
> +	if (adev->asic_type == CHIP_VEGA10 && amdgpu_sriov_runtime(adev)) {
> +		uint32_t tmp, lsb, msb, i = 0;
> +		do {
> +			tmp = RREG32_SOC15(GC, 0, mmRLC_REFCLOCK_TIMESTAMP_MSB);
> +			lsb = RREG32_SOC15(GC, 0, mmRLC_REFCLOCK_TIMESTAMP_LSB);
> +			msb = RREG32_SOC15(GC, 0, mmRLC_REFCLOCK_TIMESTAMP_MSB);
> +			i++;
> +			udelay(1);

This udelay should be conditional. In the likely case that tmp == msb, 
you should never have to delay at all. Maybe put the delay at the start 
of the loop with a condition:

     if (i != 0)
         udelay(1);

So that it only applies before the second and later loops.

Regards,
   Felix


> +		} while (unlikely(tmp != msb) && (i < adev->usec_timeout));
> +		clock = (uint64_t)lsb | ((uint64_t)msb << 32ULL);
> +	} else {
> +		WREG32_SOC15(GC, 0, mmRLC_CAPTURE_GPU_CLOCK_COUNT, 1);
> +		clock = (uint64_t)RREG32_SOC15(GC, 0, mmRLC_GPU_CLOCK_COUNT_LSB) |
> +			((uint64_t)RREG32_SOC15(GC, 0, mmRLC_GPU_CLOCK_COUNT_MSB) << 32ULL);
> +	}
>   	mutex_unlock(&adev->gfx.gpu_clock_mutex);
>   	return clock;
>   }