[PATCH] drm/amdgpu: Don't flush HDP on A+A

[Christian König]

Am 26.05.21 um 15:55 schrieb Felix Kuehling:
> Am 2021-05-25 um 1:56 p.m. schrieb Eric Huang:
>> With XGMI connection flushing HDP on PCIe is unnecessary,
>> it is also to optimize memory allocation latency.
>>
>> Signed-off-by: Eric Huang <jinhuieric.huang at amd.com>
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_cpu.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_cpu.c
>> index ac45d9c7a4e9..aefb3d2927d5 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_cpu.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_cpu.c
>> @@ -108,6 +108,8 @@ static int amdgpu_vm_cpu_update(struct
>> amdgpu_vm_update_params *p,
>>   static int amdgpu_vm_cpu_commit(struct amdgpu_vm_update_params *p,
>>                                  struct dma_fence **fence)
>>   {
>> +       if (p->adev->gmc.xgmi.connected_to_cpu)
>> +               return 0;
> I wonder if this check should be inside hdp_v4_0_flush_hdp instead so it
> catches all unnecessary HDP flushing. On the other hand, that would
> still leave the mb(). But that mb() is probably needed anyway to ensure
> that the GPU will see any previous memory writes.

Yes, that was also my concern. But it looks like my reply never made it 
to the mailing list.

I think we should have a function in amdgpu_device.c to decide if HDP 
flush/Invalidate are necessary or not.

This should then be used at all the different places where we trigger 
this (CS, GART and here).

Regards,
Christian.

>
> Regards,
>    Felix
>
>
>>          /* Flush HDP */
>>          mb();
>>          amdgpu_asic_flush_hdp(p->adev, NULL);
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