[Intel-gfx] [PATCH 3/3] drm/i915: Do not serialize forcewake acquire across domains

[Chris Wilson]

On Mon, Apr 04, 2016 at 05:51:11PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> On platforms with multiple forcewake domains it seems more efficient
> to request all desired ones and then to wait for acks to avoid
> needlessly serializing on each domain.

Not convinced since we have more machines with one domain than two. What
I did was to compact the domains array so that we only iterated over the
known set - but that feels overkill when we only have two domains today.

For the same reason (only one machine with two domains), I didn't think
seperate functions to iterate over one domain and another to iterate
over all was worth it.

What you can do though is remove an excess posting read from
fw_domains_put.

Compared to the cost of a register access (the spinlock irq mostly) the
iterator doesn't strike me as being that worthwhile an optimisation
target.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre