[Intel-gfx] [PATCH 4/9] drm/i915: Push i915_sw_fence_wait into the nonblocking atomic commit

[Daniel Vetter]

On Wed, Jul 19, 2017 at 02:04:25PM +0100, Chris Wilson wrote:
> Quoting Daniel Vetter (2017-07-19 13:54:57)
> > Blocking in a worker is ok, 
> 
> but needlessly inefficient,
> 
> > that's what the unbound_wq is for. And it
> > unifies the paths between the blocking and nonblocking commit, giving
> > me just one path where I have to implement the deadlock avoidance
> > trickery in the next patch.
> 
> For reference, I did that the other way by moving it all over to fences.

Yeah the commit message fails to explain this here:

"I first tried to implement the following patch without this rework, but
force-completing i915_sw_fence creates some serious challenges around
properly cleaning things up. So wasn't a feasible short-term approach.
Another approach would be to simple keep track of all pending atomic
commit work items and manually queue them from the reset code. With the
caveat that double-queue in case we race with the i915_sw_fence must be
avoided. Given all that, taking the cost of a double schedule in atomic
for the short-term fix is the best approach, but can be changed in the
future of course."

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch