[Intel-gfx] [PATCH v8 4/6] drm/i915: Interrupt driven fences

[Chris Wilson]

On Thu, May 12, 2016 at 10:06:34PM +0100, John.C.Harrison at Intel.com wrote:
> +void i915_gem_request_notify(struct intel_engine_cs *engine, bool fence_locked)
> +{
> +	struct drm_i915_gem_request *req, *req_next;
> +	unsigned long flags;
>  	u32 seqno;
>  
> -	seqno = req->engine->get_seqno(req->engine);
> +	if (list_empty(&engine->fence_signal_list))
> +		return;
> +
> +	if (!fence_locked)
> +		spin_lock_irqsave(&engine->fence_lock, flags);
> +
> +	if (engine->irq_seqno_barrier)
> +		engine->irq_seqno_barrier(engine);
> +	seqno = engine->get_seqno(engine);
> +
> +	list_for_each_entry_safe(req, req_next, &engine->fence_signal_list, signal_link) {

NO, NO, NO. As we said the very first time, you cannot do this from an
irq handler.

The current code is already bad enough, this is making it large constant
+ N times worse. Please do look at how to do signal driven fences in O(1)
that I posted many months ago and several times since.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre