Re: [PATCH 01/11] drm/amdgpu: Remove call to reservation_object_test_signaled_rcu before wait

["Christian König" <christian.koenig@amd.com>]

Am 29.08.2016 um 09:08 schrieb Chris Wilson:
> Since fence_wait_timeout_reservation_object_wait_timeout_rcu() with a
> timeout of 0 becomes reservation_object_test_signaled_rcu(), we do not
> need to handle such conversion in the caller. The only challenge are
> those callers that wish to differentiate the error code between the
> nonblocking busy check and potentially blocking wait.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Christian König <christian.koenig@amd.com>

Mhm, actually it was one of our developers who added the shortcut into 
reservation_object_wait_timeout_rcu().

But it looks like we forgot to clean this up in the amdgpu driver after 
doing this. So thanks for taking care of this.

Patch #1 as well as patch #6 are Reviewed-by: Christian König 
<christian.koenig@amd.com>.

For patch #6 there is also an use case for this in TTM 
ttm_bo_add_move_fence().

We could change the lock into an RCU if we can make sure that we get an 
up to date RCU protected fence and not NULL if the fence becomes freed 
right at the wrong time.

Regards,
Christian.

> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> index 88fbed2389c0..a3e6f883ac2c 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> @@ -407,10 +407,8 @@ int amdgpu_gem_wait_idle_ioctl(struct drm_device *dev, void *data,
>   		return -ENOENT;
>   	}
>   	robj = gem_to_amdgpu_bo(gobj);
> -	if (timeout == 0)
> -		ret = reservation_object_test_signaled_rcu(robj->tbo.resv, true);
> -	else
> -		ret = reservation_object_wait_timeout_rcu(robj->tbo.resv, true, true, timeout);
> +	ret = reservation_object_wait_timeout_rcu(robj->tbo.resv, true, true,
> +						  timeout);
>   
>   	/* ret == 0 means not signaled,
>   	 * ret > 0 means signaled


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