Re: [PATCH] nouveau: explicitly wait on the fence in nouveau_bo_move_m2mf

From: Salvatore Bonaccorso <carnil@debian.org>
To: Karol Herbst <kherbst@redhat.com>
Cc: linux-kernel@vger.kernel.org, Ben Skeggs <bskeggs@redhat.com>,
	Lyude Paul <lyude@redhat.com>,
	dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
	stable@vger.kernel.org,
	Computer Enthusiastic <computer.enthusiastic@gmail.com>
Subject: Re: [PATCH] nouveau: explicitly wait on the fence in nouveau_bo_move_m2mf
Date: Tue, 20 Sep 2022 12:42:03 +0200	[thread overview]
Message-ID: <YymY+3+C2aI7T3GU@eldamar.lan> (raw)
In-Reply-To: <20220819200928.401416-1-kherbst@redhat.com>

Hi,

On Fri, Aug 19, 2022 at 10:09:28PM +0200, Karol Herbst wrote:
> It is a bit unlcear to us why that's helping, but it does and unbreaks
> suspend/resume on a lot of GPUs without any known drawbacks.
> 
> Cc: stable@vger.kernel.org # v5.15+
> Closes: https://gitlab.freedesktop.org/drm/nouveau/-/issues/156
> Signed-off-by: Karol Herbst <kherbst@redhat.com>
> ---
>  drivers/gpu/drm/nouveau/nouveau_bo.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
> index 35bb0bb3fe61..126b3c6e12f9 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> @@ -822,6 +822,15 @@ nouveau_bo_move_m2mf(struct ttm_buffer_object *bo, int evict,
>  		if (ret == 0) {
>  			ret = nouveau_fence_new(chan, false, &fence);
>  			if (ret == 0) {
> +				/* TODO: figure out a better solution here
> +				 *
> +				 * wait on the fence here explicitly as going through
> +				 * ttm_bo_move_accel_cleanup somehow doesn't seem to do it.
> +				 *
> +				 * Without this the operation can timeout and we'll fallback to a
> +				 * software copy, which might take several minutes to finish.
> +				 */
> +				nouveau_fence_wait(fence, false, false);
>  				ret = ttm_bo_move_accel_cleanup(bo,
>  								&fence->base,
>  								evict, false,
> -- 
> 2.37.1
> 
> 

While this is marked for 5.15+ only, a user in Debian was seeing the
suspend issue as well on 5.10.y and did confirm the commit fixes the
issue as well in the 5.10.y series:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=989705#69

Karol, Lyude, should that as well be picked for 5.10.y?

Regards,
Salvatore