linux-kernel - Re: [PATCH 2/2] drm/nouveau/gsp: Use the sg allocator for level 2 of radix3

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Date: Mon, 29 Apr 2024 16:03:03 +1000
From: Dave Airlie <airlied@...il.com>
To: Lyude Paul <lyude@...hat.com>
Cc: nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, 
	Karol Herbst <kherbst@...hat.com>, Danilo Krummrich <dakr@...hat.com>, Daniel Vetter <daniel@...ll.ch>, 
	Dave Airlie <airlied@...hat.com>, Ben Skeggs <bskeggs@...hat.com>, Timur Tabi <ttabi@...dia.com>, 
	Dan Carpenter <dan.carpenter@...aro.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] drm/nouveau/gsp: Use the sg allocator for level 2 of radix3

> Currently, this can result in runtime PM issues on systems where memory
> Luckily, we don't actually need to allocate coherent memory for the page
> table thanks to being able to pass the GPU a radix3 page table for
> suspend/resume data. So, let's rewrite nvkm_gsp_radix3_sg() to use the sg
> allocator for level 2. We continue using coherent allocations for lvl0 and
> 1, since they only take a single page.
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> Cc: stable@...r.kernel.org
> ---
>  .../gpu/drm/nouveau/include/nvkm/subdev/gsp.h |  4 +-
>  .../gpu/drm/nouveau/nvkm/subdev/gsp/r535.c    | 71 ++++++++++++-------
>  2 files changed, 47 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h b/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h
> index 6f5d376d8fcc1..a11d16a16c3b2 100644
> --- a/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h
> +++ b/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h
> @@ -15,7 +15,9 @@ struct nvkm_gsp_mem {
>  };
>
>  struct nvkm_gsp_radix3 {
> -       struct nvkm_gsp_mem mem[3];
> +       struct nvkm_gsp_mem lvl0;
> +       struct nvkm_gsp_mem lvl1;
> +       struct sg_table lvl2;

This looks great, could we go a step further and combine lvl0 and lvl1
into a 2 page allocation, I thought we could combine lvl0/lvl1 into a
2 page alloc, but that actually might be a bad idea under memory
pressure.

Dave.