Re: [PATCH] drm/i915: Before pageflip, also wait for shared dmabuf fences.

[Mike Lothian <mike@fireburn.co.uk>]

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Hi Mario

That fixes the tearing, it's been replaced with a strange stutter, like
it's only showing half the number of frames being reported - it's really
noticeable in tomb raider

Thanks for your work on this, the stutter is much more manageable than the
tearing was

I've attached the patch that applies cleanly to 4.10-wip



On Fri, 28 Oct 2016 at 18:37 Mario Kleiner <mario.kleiner.de@gmail.com>
wrote:

>
>
> On 10/28/2016 03:34 AM, Michel Dänzer wrote:
> > On 27/10/16 10:33 PM, Mike Lothian wrote:
> >>
> >> Just another gentle ping to see where you are with this?
> >
> > I haven't got a chance to look into this any further.
> >
> >
>
> Fwiw., as a proof of concept, the attached experimental patch does work
> as tested on Intel HD Haswell + AMD R9 380 Tonga under amdgpu and
> DRI3/Present when applied to drm-next (updated from a few days ago).
> With DRI_PRIME=1 tearing for page-flipped fullscreen windows is gone
> under all loads. The tearing with "windowed" windows now looks as
> expected for regular tearing not related to Prime.
>
> ftrace confirms the i915 driver's pageflip function is waiting on the
> fence in reservation_object_wait_timeout_rcu() as it should.
>
> That entry->tv.shared needs to be set false for such buffers in
> amdgpu_bo_list_set() makes sense to me, as that is part of the buffer
> validation for command stream submission. There are other places in the
> driver where tv.shared is set, which i didn't check so far.
>
> I don't know which of these would need to be updated with a "exported
> bo" check as well, e.g., for video decoding or maybe gpu compute? Adding
> or removing the check to amdgpu_gem_va_update_vm(), e.g., made no
> difference. I assume that makes sense because that functions seems to
> deal with amdgpu internal vm page tables or page table entries for such
> a bo, not with something visible to external clients?
>
> All i can say is it fixes 3D rendering under DRI3 + Prime + pageflipping
> without causing any obvious new problems.
>
> -mario
>

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diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
index 217df24..6757b99 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
@@ -391,6 +391,7 @@ struct amdgpu_bo {
 	u64				metadata_flags;
 	void				*metadata;
 	u32				metadata_size;
+	bool				prime_exported;
 	/* list of all virtual address to which this bo
 	 * is associated to
 	 */
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
index 651115d..6e1d7b3 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
@@ -132,7 +132,10 @@ static int amdgpu_bo_list_set(struct amdgpu_device *adev,
 		entry->priority = min(info[i].bo_priority,
 				      AMDGPU_BO_LIST_MAX_PRIORITY);
 		entry->tv.bo = &entry->robj->tbo;
-		entry->tv.shared = true;
+		entry->tv.shared = !entry->robj->prime_exported;
+
+		if (entry->robj->prime_exported)
+		    DRM_DEBUG_PRIME("Exclusive fence for exported prime bo %p\n", entry->robj);
 
 		if (entry->robj->prefered_domains == AMDGPU_GEM_DOMAIN_GDS)
 			gds_obj = entry->robj;
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
index cd62f6f..54099a5 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
@@ -504,6 +504,12 @@ static void amdgpu_gem_va_update_vm(struct amdgpu_device *adev,
 
 	tv.bo = &bo_va->bo->tbo;
 	tv.shared = true;
+
+	if (bo_va->bo->prime_exported) {
+	    DRM_DEBUG_PRIME("Update for exported prime bo %p\n", bo_va->bo);
+	    /* tv.shared = false; */
+	}
+
 	list_add(&tv.head, &list);
 
 	amdgpu_vm_get_pd_bo(bo_va->vm, &list, &vm_pd);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c
index 7700dc2..bfbfeb9 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c
@@ -121,5 +121,8 @@ struct dma_buf *amdgpu_gem_prime_export(struct drm_device *dev,
 	if (amdgpu_ttm_tt_get_usermm(bo->tbo.ttm))
 		return ERR_PTR(-EPERM);
 
+	bo->prime_exported = true;
+	DRM_DEBUG_PRIME("Exporting prime bo %p\n", bo);
+
 	return drm_gem_prime_export(dev, gobj, flags);
 }

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