[Intel-gfx] [PATCH v4] drm/i915: Slaughter the thundering i915_wait_request herd

[Chris Wilson]

On Mon, Nov 30, 2015 at 02:34:40PM +0000, Chris Wilson wrote:
> +bool intel_breadcrumbs_add_waiter(struct drm_i915_gem_request *request)
> +{
> +	struct intel_breadcrumbs *b = &request->i915->breadcrumbs;
> +	struct intel_breadcrumbs_engine *be = &b->engine[request->ring->id];
> +	bool first = false;
> +
> +	spin_lock(&be->lock);
> +	if (request->waiters_count++ == 0) {
> +		struct rb_node **p, *parent;
> +
> +		if (be->first_waiter == NULL)
> +			wake_up_process(b->task);

Oh, the irony.

Converting the other side to a lockless READ_ONCE() means that I do know
have to kick after setting be->first_waiter and not rely on the spinlock
serialising the reads.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre