[Intel-gfx] Performance drop using deinterlace_vaapi on 5.19-rcX

[Daniel Vetter]

On Mon, 20 Jun 2022 at 17:28, Christian König <christian.koenig at amd.com> wrote:
>
> Hi Thomas,
>
> Am 20.06.22 um 16:31 schrieb Thomas Voegtle:
> > On Mon, 20 Jun 2022, Christian König wrote:
> >
> >> Am 20.06.22 um 13:40 schrieb Thomas Voegtle:
> >>>  On Mon, 20 Jun 2022, Christian König wrote:
> >>>
> >>>>  Hi Thomas,
> >>>>
> >>>>  [moving vger to bcc]
> >>>>
> >>>>  mhm, sounds like something isn't running in parallel any more.
> >>>>
> >>>>  We usually don't test the multimedia engines for this but we do test
> >>>>  gfx+compute, so I'm really wondering what goes wrong here.
> >>>>
> >>>>  Could you run some tests for me? Additional to that I'm going to
> >>>> raise
> >>>>  that issue with our multimedia guys later today.
> >>>
> >>>  Yes, I can run some tests for you. Which tests?
> >>
> >> Try this as root:
> >>
> >> echo 1 >
> >> /sys/kernel/debug/tracing/events/dma_fence/dma_fence_init/enable
> >> echo 1 >
> >> /sys/kernel/debug/tracing/events/dma_fence/dma_fence_signaled/enable
> >> cat /sys/kernel/debug/tracing/trace_pipe > trace.log
> >>
> >> Then start the encoding in another shell, after it completed cancel
> >> the cat with cntr+c and save the log file.
> >>
> >> Do this one with the old kernel and once with the new one.
> >
> >
> > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2F32h.de%2Ftv%2F5.18.0-i5-trace.log.bz2&data=05%7C01%7Cchristian.koenig%40amd.com%7C41a052960a4d4f7dd38e08da52c99097%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637913323382588469%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=xv8vLUuBq37sBFcGxdua%2FnNQ51BiN1USn30ehP8bys0%3D&reserved=0
> > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2F32h.de%2Ftv%2F5.19.0-rc3-i5-trace.log.bz2&data=05%7C01%7Cchristian.koenig%40amd.com%7C41a052960a4d4f7dd38e08da52c99097%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637913323382588469%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=xuBVrQMQ%2FDK3Gv1qN%2FntJ9NjXOZxD6XVkmDCWfG4K44%3D&reserved=0
> >
> >
> > I hope I have done this correctly.
> > All necessary tracing things switched on?
>
> Yeah, that looks like what I wanted to see.
>
> >
> > I want to add that this is a headless machine. No monitor connected.
> >
>
> I've just realized that you aren't even using any AMD GPU for
> transcoding, so I have no idea why removing the AMD specific workaround
> can cause a performance problem for i915.
>
> It must be somehow related to i915 now adding some additional
> synchronization in between submissions.
>
> Adding the Intel mailing list, maybe somebody has a better idea.

Only thing I can spot is that we now pile up USAGE_WRITE fences, but
beforehand they got replaced. Also the deinterlace stuff means libva
uses render engine, so this kinda fits - without using the render
engine it's just a single engine, and hence you should never have
multiple write fences (not logically, but hsw is a ringbuffer and i915
doesn't have a ringbuffer scheduler, so it's all in-order anyway and
hence not possible to change something).

This would mean that i915 is doing something silly (well not obeying
the old dma_resv rules that any new exclusive fence must be a strict
superset of all currently attached fences), which it totally is doing
with the EXEC_OBJECT_ASYNC flag. But libva doesn't use that.

So tbh I have no idea, but maybe a quick hack that tosses any old
USAGE_WRITE fence like the old dma_resv_add_excl_fence did would sched
some light?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch