[Intel-gfx] [PATCH 7/9] drm/i915/execlists: Reduce lock context between schedule/submit_request

[Chris Wilson]

On Fri, May 05, 2017 at 02:30:08PM +0100, Tvrtko Ursulin wrote:
> 
> On 03/05/2017 12:37, Chris Wilson wrote:
> >If we do not require to perform priority bumping, and we haven't yet
> >submitted the request, we can update its priority in situ and skip
> >acquiring the engine locks -- thus avoiding any contention between us
> >and submit/execute.
> >
> >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >---
> > drivers/gpu/drm/i915/intel_lrc.c | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> >
> >diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> >index fb0025627676..ca7f28795e2d 100644
> >--- a/drivers/gpu/drm/i915/intel_lrc.c
> >+++ b/drivers/gpu/drm/i915/intel_lrc.c
> >@@ -767,6 +767,17 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
> > 		list_safe_reset_next(dep, p, dfs_link);
> > 	}
> >
> >+	/* If we didn't need to bump any existing priorites, and we haven't
> 
> priorities
> 
> >+	 * yet submitted this request (i..e there is no porential race with
> 
> potential
> 
> >+	 * execlists_submit_request()), we can set our own priority and skip
> >+	 * acquiring the engine locks.
> >+	 */
> >+	if (request->priotree.priority == INT_MIN) {
> >+		request->priotree.priority = prio;
> >+		if (stack.dfs_link.next == stack.dfs_link.prev)
> >+			return;
> 
> Move the assignment of the priority under the if?

The assignment always work. I just liked the look of this code more :)
The skip of the assignment is minor benefit. For bonus points, could do
a list_del_entry(&stack.dfs_link) after the return.

Sold.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre