[PATCH] drm/amdgpu: Raise dma resv usage for created TLB fence

[Christian König]

Well that explanation doesn't seem to make much sense either.

What do you mean with TLB flush is occurring prematurely?

Regards,
Christian.

Am 05.09.24 um 14:38 schrieb Andjelkovic, Dejan:
>
> [AMD Official Use Only - AMD Internal Distribution Only]
>
>
> Hi there. We're running into a page fault issue that's very easily 
> reproducible on a SRIOV environment when using SDMA for page table 
> updates. Going through mapping logs and trace files, it seems TLB 
> flush is occurring prematurely. Changing the usage to KERNEL 
> completely stops the page fault from occurring with no performance 
> impact, which was confirmed with extensive testing. Looking through 
> amdgpu_vm_sdma.c, namely within amdgpu_vm_sdma_update when waiting for 
> PD/PT moves to be completed, fences are iterated with KERNEL usage 
> specified which are then added as a job dependency.
>
> Best regards,
> Dejan
> ------------------------------------------------------------------------
> *From:* Koenig, Christian <Christian.Koenig at amd.com>
> *Sent:* Thursday, September 5, 2024 1:17 PM
> *To:* Andjelkovic, Dejan <Dejan.Andjelkovic at amd.com>; 
> amd-gfx at lists.freedesktop.org <amd-gfx at lists.freedesktop.org>
> *Cc:* Prica, Nikola <Nikola.Prica at amd.com>; Kuehling, Felix 
> <Felix.Kuehling at amd.com>; Deng, Emily <Emily.Deng at amd.com>
> *Subject:* Re: [PATCH] drm/amdgpu: Raise dma resv usage for created 
> TLB fence
> Am 05.09.24 um 10:58 schrieb Dejan Andjelkovic:
> > When using SDMA for PT updates, a TLB fence hooked to a buffer
> > objects dma resv object with usage declared as BOOKKEEP leaves a
> > chance for TLB flush to occur prematurely. This will lead to a page
> > fault. Raising the usage from BOOKKEEP to KERNEL removes this
> > possibility.
>
> Well that's complete nonsense. The usage model is for implicit syncing
> and not even remotely related to TLB flushing.
>
> What exactly is the problem you run into?
>
> Regards,
> Christian.
>
> >
> > Signed-off-by: Dejan Andjelkovic <Dejan.Andjelkovic at amd.com>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c 
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > index f93804902fd3..8efc2cf9bbb0 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > @@ -928,7 +928,7 @@ amdgpu_vm_tlb_flush(struct 
> amdgpu_vm_update_params *params,
> >
> >                /* Makes sure no PD/PT is freed before the flush */
> > dma_resv_add_fence(vm->root.bo->tbo.base.resv, *fence,
> > - DMA_RESV_USAGE_BOOKKEEP);
> > + DMA_RESV_USAGE_KERNEL);
> >        }
> >   }
> >
>
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