[Intel-gfx] [PATCH] drm/i915/execlists: Use a local lock for dfs_link access

[Chris Wilson]

On Wed, Nov 16, 2016 at 03:54:23PM +0000, Tvrtko Ursulin wrote:
> 
> On 16/11/2016 15:27, Chris Wilson wrote:
> >Avoid requiring struct_mutex for exclusive access to the temporary
> >dfs_link inside the i915_dependency as not all callers may want to touch
> >struct_mutex. So rather than force them to take a highly contended
> >lock, introduce a local lock for the execlists schedule operation.
> >
> >Reported-by: David Weinehall <david.weinehall at linux.intel.com>
> >Fixes: 9a151987d709 ("drm/i915: Add execution priority boosting for mmioflips")
> 
> Grumble grumble, sloppy review. :I

Too busy living the good life with working atomic flips.
 
> >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >Cc: David Weinehall <david.weinehall at linux.intel.com>
> >---
> > drivers/gpu/drm/i915/intel_lrc.c | 7 +++++--
> > 1 file changed, 5 insertions(+), 2 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> >index e23b6a2600fb..10e59ff0d8f1 100644
> >--- a/drivers/gpu/drm/i915/intel_lrc.c
> >+++ b/drivers/gpu/drm/i915/intel_lrc.c
> >@@ -694,6 +694,7 @@ pt_lock_engine(struct i915_priotree *pt, struct intel_engine_cs *locked)
> >
> > static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
> > {
> >+	static DEFINE_MUTEX(lock);
> 
> Good enough for one GPU. :) Consider improving in the future as it
> is not in the spirit of the driver.

Actually... Being able to PI across multiple GPUs is part of the dream.
In that case, it does need to be a global lock - just a bit iffy on
getting dependency tracking into a common layer.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre