Re: [PATCH v2 1/2] drm/i915: Do an unlocked wait before set-cache-level ioctl

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Since a change in cache level is likely to trigger an unbind, avoid
> waiting under the mutex by preemptively doing an unlocked wait.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 29 +++++++++++++++++++----------
>  1 file changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index c1c2765bb8d0..0926c291404c 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3384,7 +3384,7 @@ int i915_gem_set_caching_ioctl(struct drm_device *dev, void *data,
>  	struct drm_i915_gem_caching *args = data;
>  	struct drm_i915_gem_object *obj;
>  	enum i915_cache_level level;
> -	int ret;
> +	int ret = 0;
>  
>  	switch (args->caching) {
>  	case I915_CACHING_NONE:
> @@ -3409,20 +3409,29 @@ int i915_gem_set_caching_ioctl(struct drm_device *dev, void *data,
>  		return -EINVAL;
>  	}
>  
> -	ret = i915_mutex_lock_interruptible(dev);
> +	obj = i915_gem_object_lookup(file, args->handle);
> +	if (!obj)
> +		return -ENOENT;
> +
> +	if (obj->cache_level == level)
> +		goto out;
> +
> +	ret = i915_gem_object_wait(obj,
> +				   I915_WAIT_INTERRUPTIBLE,
> +				   MAX_SCHEDULE_TIMEOUT,
> +				   to_rps_client(file));
>  	if (ret)
> -		return ret;
> +		goto out;
>  
> -	obj = i915_gem_object_lookup(file, args->handle);
> -	if (!obj) {
> -		ret = -ENOENT;
> -		goto unlock;
> -	}

Is the intent here that you just make it very likely
that the wait in set_cache_level will not trigger?

-Mika

> +	ret = i915_mutex_lock_interruptible(dev);
> +	if (ret)
> +		goto out;
>  
>  	ret = i915_gem_object_set_cache_level(obj, level);
> -	i915_gem_object_put(obj);
> -unlock:
>  	mutex_unlock(&dev->struct_mutex);
> +
> +out:
> +	i915_gem_object_put(obj);
>  	return ret;
>  }
>  
> -- 
> 2.11.0
>
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