[PATCH 1/3] drm/amdgpu: implicitly sync the dependent read fences

[Liang, Prike]

[Public]

> From: Liang, Prike
> Sent: Friday, April 25, 2025 3:44 PM
> To: Yadav, Arvind <Arvind.Yadav at amd.com>; amd-gfx at lists.freedesktop.org
> Cc: Deucher, Alexander <Alexander.Deucher at amd.com>; Koenig, Christian
> <Christian.Koenig at amd.com>
> Subject: RE: [PATCH 1/3] drm/amdgpu: implicitly sync the dependent read fences
>
> > From: Yadav, Arvind <Arvind.Yadav at amd.com>
> > Sent: Friday, April 25, 2025 3:21 PM
> > To: Liang, Prike <Prike.Liang at amd.com>; amd-gfx at lists.freedesktop.org
> > Cc: Deucher, Alexander <Alexander.Deucher at amd.com>; Koenig, Christian
> > <Christian.Koenig at amd.com>
> > Subject: Re: [PATCH 1/3] drm/amdgpu: implicitly sync the dependent
> > read fences
> >
> > This is problem for TLB flush. We should not do this changes. Here we
> > are utilizing DMA_RESV_USAGE_BOOKKEEP due to the TLB flush fence
> > associated with the page table (PT). We are ensuring that no page
> > directory (PD) or page table (PT) should be free before flush and ttm
> > bo release and delete both are also waiting for BOOKKEEP fence. Please drop
> this changes for eviction fence.
> Thanks for sharing the background. So, we may need to test the fence whether is
> an eviction fence in amdgpu_sync_test_fence () before added it to the VM sync.
It looks the TLB flush fence only added to the VM BO reservation and requires a sync at compute VM.
As to the VM reservation sync whether can return and sync to the DMA_RESV_USAGE_READ, and I will
further check it separately with the eviction fence release. As to the eviction fence sync problem issue, I would like
to put exclude the eviction fence sync at amdgpu_sync_test_fence().

Thanks,
Prike
> Thanks,
> Prike
> > Regards,
> > ~arvind
> >
> > On 4/25/2025 12:37 PM, Prike Liang wrote:
> > > The driver doesn't want to sync on the DMA_RESV_USAGE_BOOKKEEP
> usage
> > > fences, so here only return and sync the dependent read fences.
> > >
> > > Signed-off-by: Prike Liang <Prike.Liang at amd.com>
> > > ---
> > >   drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c | 5 ++---
> > >   1 file changed, 2 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c
> > > b/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c
> > > index 5576ed0b508f..4e1d30ecb6cc 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c
> > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c
> > > @@ -249,9 +249,8 @@ int amdgpu_sync_resv(struct amdgpu_device *adev,
> > > struct amdgpu_sync *sync,
> > >
> > >           if (resv == NULL)
> > >                   return -EINVAL;
> > > -
> > > - /* TODO: Use DMA_RESV_USAGE_READ here */
> > > - dma_resv_for_each_fence(&cursor, resv,
> > DMA_RESV_USAGE_BOOKKEEP, f) {
> > > + /*Only return and sync the fences of usage <=
> > DMA_RESV_USAGE_READ.*/
> > > + dma_resv_for_each_fence(&cursor, resv, DMA_RESV_USAGE_READ, f) {
> > >                   dma_fence_chain_for_each(f, f) {
> > >                           struct dma_fence *tmp = dma_fence_chain_contained(f);
> > >