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

[Chris Wilson]

On Thu, Jan 19, 2017 at 01:42:47PM +0200, Mika Kuoppala wrote:
> Chris Wilson <chris at 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 at 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);
> 
> Does this need to be i915_gem_object_lookup_rcu?

No. That's a special case for when the caller knows it is using RCU for
the entire duration of the access and so doesn't need to acquire a
reference to the object.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre