On 28/02/2019 09:43, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2019-02-28 09:38:36)
On 28/02/2019 08:29, Chris Wilson wrote:
@@ -143,7 +141,15 @@ static u32 __i915_gem_park(struct drm_i915_private *i915)
intel_display_power_put(i915, POWER_DOMAIN_GT_IRQ, wakeref);
- return i915->gt.epoch;
+ /*
+ * When we are idle, it is an opportune time to reap our caches.
+ * However, we have many objects that utilise RCU and the ordered
+ * i915->wq that this work is executing on. To try and flush any
+ * pending frees now we are idle, we first wait for an RCU grace
+ * period, and then queue a task (that will run last on the wq) to
+ * shrink and re-optimize the caches.
+ */
+ i915_globals_park();
I think this comment would be better placed in i915_globals_park.
In i915_globals_park(), we have
/*
* Defer shrinking the global slab caches (and other work) until
* after a RCU grace period has completed with no activity. This
* is to try and reduce the latency impact on the consumers caused
* by us shrinking the caches the same time as they are trying to
* allocate, with the assumption being that if we idle long enough
* for an RCU grace period to elapse since the last use, it is likely
* to be longer until we need the caches again.
*/
Yeah, the old comment is a bit too verbose now, but I think it's still
worth having a comment there to explain what's about to be done and why
we call it now.
/* Tell the world we are idle and reap the benefits! */
Too subtle?
Maybe even no comment needed (gasp!). When I looks at the function I see:
__i915_gem_park(...)
{
...
intel_engines_park(i915);
i915_timelines_park(i915);
i915_pmu_gt_parked(i915);
i915_vma_parked(i915);
...
i915_globals_park();
...
}
So it seems pretty obvious different components are parked from here. :)
Regards,
Tvrtko
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