[Intel-gfx] [PATCH 2/3] drm/i915: add the FBC mutex

[Chris Wilson]

On Wed, Jun 17, 2015 at 04:39:32PM -0300, Paulo Zanoni wrote:
> 2015-06-17 4:52 GMT-03:00 Chris Wilson <chris at chris-wilson.co.uk>:
> > These busy bits are locked higher up. In fact I want to migrate that
> > lock to a spinlock, which has implications here. I didn't see anything
> > that mandated using a mutex for fbc, right?
> 
> I didn't understand your idea. You want to replace the whole FBC mutex
> for a spinlock? Why?

I want to replace the frontbuffer mutex with a spinlock. You are
inserting a mutex under my intended spinlock, which blows my idea of
trying to speed up the normal operations.
 
> Please notice that we have dev_priv->fbc.busy_bits and also
> dev_priv->fb_tracking.busy_bits. The FBC busy bits are only handled in
> the intel_fbc.c functions. So maybe you want the spilock around the
> fb_tracking ones? That wouldn't require changing the FBC mutex to a
> spinlock, and it could be done today.

Somehow I need to avoid the mutex here, so kicking off the fbc
enable/disable needs to be lockless (or spinlocked at most). Of course,
if that is not practical, I will just have to live with not converting
the higher mutex into the spinlock.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre