[Intel-gfx] [PATCH 6/9] drm/i915: Split execlist priority queue into rbtree + linked list

[Chris Wilson]

On Fri, May 05, 2017 at 02:37:41PM +0100, Tvrtko Ursulin wrote:
> 
> On 05/05/2017 14:32, Chris Wilson wrote:
> >On Fri, May 05, 2017 at 02:19:07PM +0100, Tvrtko Ursulin wrote:
> >>
> >>On 03/05/2017 12:37, Chris Wilson wrote:
> >>>struct intel_engine_cs {
> >>>@@ -367,6 +373,7 @@ struct intel_engine_cs {
> >>>
> >>>	/* Execlists */
> >>>	struct tasklet_struct irq_tasklet;
> >>>+	struct execlist_priolist default_priolist;
> >>>	struct execlist_port {
> >>>		struct drm_i915_gem_request *request_count;
> >>>#define EXECLIST_COUNT_BITS 2
> >>>
> >
> >Just a small bikeshed to consider. Having switched to
> >I915_PRIORITY_NORMAL, do we have a better name for default_priolist? I
> >still prefer default_priolist over normal_priolist. Go back to
> >I915_PRIORITY_DEFAULT?
> 
> default_priolist is fine I think since it is dual purpose. Primary
> purpose to avoid allocations as you said.
> 
> Although I am still a bit dejected how some userspace could decide
> one day to send everything at I915_PRIORITY_NORMAL - n, in order to
> use I915_PRIORITY_NORMAL as the high prio not requiring
> cap_sys_admin, and in doing so completely defeat the atomic kmalloc
> avoidance. :(

Should we just bite the bullet and install a kmem_cache here?
It didn't solve the kmalloc error handling, but it does at least give us
a freelist. There is a reasonable argument that as soon as userspace
starts using non-default priorities, we may see many different levels
justifying allocating a whole slab upfront.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre