Re: [PATCH] drm/amdgpu: fix ocl test performance drop

[zhoucm1 <david1.zhou-5C7GfCeVMHo@public.gmane.org>]

I also realized this problem when I did fix for sched fence, I thought 
if no issue, just left it as current code, it's more safe.
As Flora point it out, it results in performance drop, then we need to 
correct it back.
pipeline_sync in vm flush should be inserted only when 
amdgpu_vm_ring_has_compute_vm_bug() is true, not all time for every vm 
flush for all engines. The bug has been fixed in mec firmware from 
version 673 in gfx8.
About gfx9 for amdgpu_vm_ring_has_compute_vm_bug(), current 
implementation is thinking gfx9 doesn't have compute vm bug by default. 
Not sure it's in there. If no vm fault related to this bug, then we can 
think gfx9 has no compute vm bug, I believe firmware team does that 
based on previous generation, otherwise we need identify every 
generation, that's crazy.

Regards,
David Zhou
On 2017年05月19日 11:36, Flora Cui wrote:
> btw, what's about gfx9 for amdgpu_vm_ring_has_compute_vm_bug()? Is the
> workaround still needed?
>
> On Fri, May 19, 2017 at 10:25:19AM +0800, Flora Cui wrote:
>> On Thu, May 18, 2017 at 01:38:15PM +0200, Christian König wrote:
>>> Am 18.05.2017 um 09:45 schrieb Flora Cui:
>>>> partial revert commit <6971d3d> - drm/amdgpu: cleanup logic in
>>>> amdgpu_vm_flush
>>>>
>>>> Change-Id: Iadce9d613dfe9a739643a74050cea55854832adb
>>>> Signed-off-by: Flora Cui <Flora.Cui@amd.com>
>>> I don't see how the revert should be faster than the original.
>>>
>>> Especially that amdgpu_vm_had_gpu_reset() is now called twice sounds like
>>> more overhead than necessary.
>>>
>>> Please explain further.
>>>
>>> Christian.
>>>
>>>> ---
>>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 14 +++++---------
>>>>   1 file changed, 5 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>>> index 88420dc..a96bad6 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>>> @@ -743,23 +743,19 @@ int amdgpu_vm_flush(struct amdgpu_ring *ring, struct amdgpu_job *job)
>>>>   		id->gws_size != job->gws_size ||
>>>>   		id->oa_base != job->oa_base ||
>>>>   		id->oa_size != job->oa_size);
>>>> -	bool vm_flush_needed = job->vm_needs_flush ||
>>>> -		amdgpu_vm_ring_has_compute_vm_bug(ring);
>>>>   	unsigned patch_offset = 0;
>>>>   	int r;
>>>> -	if (amdgpu_vm_had_gpu_reset(adev, id)) {
>>>> -		gds_switch_needed = true;
>>>> -		vm_flush_needed = true;
>>>> -	}
>>>> -
>>>> -	if (!vm_flush_needed && !gds_switch_needed)
>>>> +	if (!job->vm_needs_flush && !gds_switch_needed &&
>>>> +	    !amdgpu_vm_had_gpu_reset(adev, id) &&
>>>> +	    !amdgpu_vm_ring_has_compute_vm_bug(ring))
>>>>   		return 0;
>>>>   	if (ring->funcs->init_cond_exec)
>>>>   		patch_offset = amdgpu_ring_init_cond_exec(ring);
>>>> -	if (ring->funcs->emit_vm_flush && vm_flush_needed) {
>> [flora]: for compute ring & amdgpu_vm_ring_has_compute_vm_bug(), a vm_flush is
>> inserted. This might cause performance drop.
>>>> +	if (ring->funcs->emit_vm_flush &&
>>>> +	    (job->vm_needs_flush || amdgpu_vm_had_gpu_reset(adev, id))) {
>>>>   		struct fence *fence;
>>>>   		trace_amdgpu_vm_flush(ring, job->vm_id, job->vm_pd_addr);
>>>
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