AMDGPU's rings VS Radeon's

[Alexandre Demers]

On Mon, Aug 11, 2025 at 6:22 PM Alex Deucher <alexdeucher at gmail.com> wrote:

> On Mon, Aug 11, 2025 at 6:08 PM Alexandre Demers
> <alexandre.f.demers at gmail.com> wrote:
> >
> > Hi,
> >
> > For those who know, I'm still working on VCE1 enablement under AMDGPU.
> Progress is happening, slowly but surely. While investigating the ring init
> calls, a few elements catched my attention and I'd like some help in
> figuring out the differences between AMDGPU's ring sizes and Radeon's ones.
> >
> > 1- I understand that the size parameter changed from bytes under
> radeon_ring_init to dword under amdgpu_ring_init. That being said, some
> values don't seem to be equivalent between Radeon and AMDGPU. For example,
> GFX ring size went from 1024 * 1024 bytes to 1024 dwords (for most GFX
> versions), which seems off even when taking into account how
> amdgpu_ring_init calculates the final allocated size. This question is more
> about understanding than a problem strictly speaking.
>
> You can make the ring any size you want.  It's specified in the queue
> descriptor.  I don't remember why we picked the sizes we did in radeon
> off hand.
>
> OK, thanks

> >
> > 2- Under AMDGPU, SI's GFX (GFX6) ring size is 2048, while this value is
> 1024 for all the other GFX versions. Under Radeon, the GFX ring size values
> are all the same (1024 * 1024) under Evergreen/SI/CIK/NI and others. Is
> there any reason why SI's GFX6 ring size would be twice the size of the
> other values under AMDGPU?
> >
>
> From the git history:
> commit 97041ed37718dc9ba30aa23ca74093dc93ac89fb
> Author: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
> Date:   Thu Apr 13 16:22:51 2023 +0200
>
>     drm/amdgpu: Increase GFX6 graphics ring size.
>
>     To ensure it supports 192 IBs per submission, so we can keep a
>     simplified IB limit in the follow up patch without having to
>     look at IP or GPU version.
>
>     Reviewed-by: Christian König <christian.koenig at amd.com>
>     Signed-off-by: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
>     Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
>
>
>
> > 3- Would it be acceptable to add names to rings under Radeon, the same
> names as the ones used under AMDGPU? I think it is more talkative for the
> average user and for debugging purposes to deal with ring names than
> indexes. I already have patches in my code to address this suggestion.
> >
>
> If you think there is value there.  It seems like it would generate a
> lot of churn in that driver for little gain.
>
> Alex
>
> The patches are pretty simple and straightforward. I'll send them.

Cheers!

Alexandre Demers

> That's all for now.
> >
> > Cheers
> > Alexandre Demers
>
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