[PATCH] nouveau: rip out busy fence waits

[Danilo Krummrich]

On 4/17/24 07:40, Dave Airlie wrote:
> From: Dave Airlie <airlied at redhat.com>
> 
> I'm pretty sure this optimisation is actually not a great idea,
> and is racy with other things waiting for fences.

Yes, I tried to use it in the past on scheduler tear down, to have an
indicator whether all jobs had the chance to finish.

However, it happened that using a CPU busy loop saw the fence as signaled,
while an (event based) dma_fence was still seen as unsignaled.

> 
> Just nuke it, there should be no need to do fence waits in a
> busy CPU loop.
> 
> Signed-off-by: Dave Airlie <airlied at redhat.com>

Applied to drm-misc-next.

> ---
>   drivers/gpu/drm/nouveau/nouveau_bo.c    |  2 +-
>   drivers/gpu/drm/nouveau/nouveau_chan.c  |  2 +-
>   drivers/gpu/drm/nouveau/nouveau_dmem.c  |  2 +-
>   drivers/gpu/drm/nouveau/nouveau_fence.c | 30 +------------------------
>   drivers/gpu/drm/nouveau/nouveau_fence.h |  2 +-
>   drivers/gpu/drm/nouveau/nouveau_gem.c   |  2 +-
>   6 files changed, 6 insertions(+), 34 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
> index 8a30f5a0525b..a4e8f625fce6 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> @@ -902,7 +902,7 @@ nouveau_bo_move_m2mf(struct ttm_buffer_object *bo, int evict,
>   	 * 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);
> +	nouveau_fence_wait(fence, false);
>   	ret = ttm_bo_move_accel_cleanup(bo, &fence->base, evict, false,
>   					new_reg);
>   	nouveau_fence_unref(&fence);
> diff --git a/drivers/gpu/drm/nouveau/nouveau_chan.c b/drivers/gpu/drm/nouveau/nouveau_chan.c
> index 7c97b2886807..66fca95c10c7 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_chan.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_chan.c
> @@ -72,7 +72,7 @@ nouveau_channel_idle(struct nouveau_channel *chan)
>   
>   		ret = nouveau_fence_new(&fence, chan);
>   		if (!ret) {
> -			ret = nouveau_fence_wait(fence, false, false);
> +			ret = nouveau_fence_wait(fence, false);
>   			nouveau_fence_unref(&fence);
>   		}
>   
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index 12feecf71e75..033a09cd3c8f 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -128,7 +128,7 @@ static void nouveau_dmem_page_free(struct page *page)
>   static void nouveau_dmem_fence_done(struct nouveau_fence **fence)
>   {
>   	if (fence) {
> -		nouveau_fence_wait(*fence, true, false);
> +		nouveau_fence_wait(*fence, false);
>   		nouveau_fence_unref(fence);
>   	} else {
>   		/*
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
> index c3ea3cd933cd..8de941379324 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> @@ -312,39 +312,11 @@ nouveau_fence_wait_legacy(struct dma_fence *f, bool intr, long wait)
>   	return timeout - t;
>   }
>   
> -static int
> -nouveau_fence_wait_busy(struct nouveau_fence *fence, bool intr)
> -{
> -	int ret = 0;
> -
> -	while (!nouveau_fence_done(fence)) {
> -		if (time_after_eq(jiffies, fence->timeout)) {
> -			ret = -EBUSY;
> -			break;
> -		}
> -
> -		__set_current_state(intr ?
> -				    TASK_INTERRUPTIBLE :
> -				    TASK_UNINTERRUPTIBLE);
> -
> -		if (intr && signal_pending(current)) {
> -			ret = -ERESTARTSYS;
> -			break;
> -		}
> -	}
> -
> -	__set_current_state(TASK_RUNNING);
> -	return ret;
> -}
> -
>   int
> -nouveau_fence_wait(struct nouveau_fence *fence, bool lazy, bool intr)
> +nouveau_fence_wait(struct nouveau_fence *fence, bool intr)
>   {
>   	long ret;
>   
> -	if (!lazy)
> -		return nouveau_fence_wait_busy(fence, intr);
> -
>   	ret = dma_fence_wait_timeout(&fence->base, intr, 15 * HZ);
>   	if (ret < 0)
>   		return ret;
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.h b/drivers/gpu/drm/nouveau/nouveau_fence.h
> index bc13110bdfa4..88213014b675 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fence.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.h
> @@ -23,7 +23,7 @@ void nouveau_fence_unref(struct nouveau_fence **);
>   
>   int  nouveau_fence_emit(struct nouveau_fence *);
>   bool nouveau_fence_done(struct nouveau_fence *);
> -int  nouveau_fence_wait(struct nouveau_fence *, bool lazy, bool intr);
> +int  nouveau_fence_wait(struct nouveau_fence *, bool intr);
>   int  nouveau_fence_sync(struct nouveau_bo *, struct nouveau_channel *, bool exclusive, bool intr);
>   
>   struct nouveau_fence_chan {
> diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c b/drivers/gpu/drm/nouveau/nouveau_gem.c
> index 49c2bcbef129..f715e381da69 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
> @@ -928,7 +928,7 @@ nouveau_gem_ioctl_pushbuf(struct drm_device *dev, void *data,
>   	}
>   
>   	if (sync) {
> -		if (!(ret = nouveau_fence_wait(fence, false, false))) {
> +		if (!(ret = nouveau_fence_wait(fence, false))) {
>   			if ((ret = dma_fence_get_status(&fence->base)) == 1)
>   				ret = 0;
>   		}