Re: [PATCH] drm/amdgpu: Ignore KFD eviction fences invalidating preemptible DMABuf imports

[Felix Kuehling <felix.kuehling@xxxxxxx>]

Am 2023-04-13 um 07:35 schrieb Christian König:
> Am 13.04.23 um 03:01 schrieb Felix Kuehling:
> > Am 2023-04-12 um 18:25 schrieb Eric Huang:
> > > It is to avoid redundant eviction for KFD's DMAbuf import
> > > bo when dmaunmapping DMAbuf. The DMAbuf import bo has
> > > been set as AMDGPU_PL_PREEMPT in KFD when mapping.
> > >
> > > Signed-off-by: Eric Huang <jinhuieric.huang@xxxxxxx>
> >
> > Reviewed-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
> >
> > I'd like to get an Acked-by from Christian as well before submitting 
> > this.
>
> I have to admit that I only partially followed the internal 
> discussion, but in general you need a *really* good explanation for this.
>
> E.g. add code comment and explain in the commit message extensively 
> why this is needed and why there are no alternatives.

OK. I'll give it a shot:

   This code path is used among other things when invalidating DMABuf
   imports. These imports share a reservation object with the exported
   BO. Waiting on all the fences in this reservation will trigger KFD
   eviction fences unnecessarily, for example when a DMABuf import for
   a DMA mapping on a secondary GPU is being unmapped explicitly. Only
   moving the original exported BO requires stopping KFD user mode
   queues. If the invalidation is triggered through a move notifier
   from the exported BO, then moving the original BO already triggered
   the eviction fence and we don't need to wait for it again on the import.

   We can identify DMABuf imports in KFD for secondary GPU DMA mappings
   by the mem_type AMDGPU_PL_PREEMPT. In this case, use a wait
   operation that ignores KFD eviction fences.

How does this sound?

Regards,
  Felix


> Regards,
> Christian.
>
> > Thanks,
> >   Felix
> >
> >
> > > ---
> > >   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 7 ++++++-
> > >   1 file changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c 
> > > b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> > > index 2430f3e9f3a7..64795fe9eecb 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> > > @@ -526,7 +526,12 @@ static int amdgpu_bo_move(struct 
> > > ttm_buffer_object *bo, bool evict,
> > >       if ((old_mem->mem_type == TTM_PL_TT ||
> > >            old_mem->mem_type == AMDGPU_PL_PREEMPT) &&
> > >           new_mem->mem_type == TTM_PL_SYSTEM) {
> > > -        r = ttm_bo_wait_ctx(bo, ctx);
> > > +        if (old_mem->mem_type == AMDGPU_PL_PREEMPT)
> > > +            r = amdgpu_bo_sync_wait(abo,
> > > +                        AMDGPU_FENCE_OWNER_KFD,
> > > +                        ctx->interruptible);
> > > +        else
> > > +            r = ttm_bo_wait_ctx(bo, ctx);
> > >           if (r)
> > >               return r;