On 29/06/2018 08:53, Chris Wilson wrote:
Taken from an idea used for FQ_CODEL, we give new request flows a
priority boost. These flows are likely to correspond with interactive
tasks and so be more latency sensitive than the long queues. As soon as
the client has more than one request in the queue, further requests are
not boosted and it settles down into ordinary steady state behaviour.
Such small kicks dramatically help combat the starvation issue, by
allowing each client the opportunity to run even when the system is
under heavy throughput load (within the constraints of the user
selected priority).
Any effect on non-micro benchmarks to mention in the commit message as
the selling point?
Testcase: igt/benchmarks/rrul
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_request.c | 16 ++++++++++++++--
drivers/gpu/drm/i915/i915_scheduler.h | 4 +++-
2 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 14bf0be6f994..2d7a785dd88c 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -1052,8 +1052,20 @@ void i915_request_add(struct i915_request *request)
*/
local_bh_disable();
rcu_read_lock(); /* RCU serialisation for set-wedged protection */
- if (engine->schedule)
- engine->schedule(request, &request->gem_context->sched);
+ if (engine->schedule) {
+ struct i915_sched_attr attr = request->gem_context->sched;
+
+ /*
+ * Boost priorities to new clients (new request flows).
+ *
+ * Allow interactive/synchronous clients to jump ahead of
+ * the bulk clients. (FQ_CODEL)
+ */
+ if (!prev || i915_request_completed(prev))
+ attr.priority |= I915_PRIORITY_NEWCLIENT;
Now a "lucky" client can always get higher priority an keep preempting
everyone else by just timing it's submissions right. So I have big
reservations on this one.
Regards,
Tvrtko
+
+ engine->schedule(request, &attr);
+ }
rcu_read_unlock();
i915_sw_fence_commit(&request->submit);
local_bh_enable(); /* Kick the execlists tasklet if just scheduled */
diff --git a/drivers/gpu/drm/i915/i915_scheduler.h b/drivers/gpu/drm/i915/i915_scheduler.h
index 7edfad0abfd7..e9fb6c1d5e42 100644
--- a/drivers/gpu/drm/i915/i915_scheduler.h
+++ b/drivers/gpu/drm/i915/i915_scheduler.h
@@ -19,12 +19,14 @@ enum {
I915_PRIORITY_INVALID = INT_MIN
};
-#define I915_USER_PRIORITY_SHIFT 0
+#define I915_USER_PRIORITY_SHIFT 1
#define I915_USER_PRIORITY(x) ((x) << I915_USER_PRIORITY_SHIFT)
#define I915_PRIORITY_COUNT BIT(I915_USER_PRIORITY_SHIFT)
#define I915_PRIORITY_MASK (-I915_PRIORITY_COUNT)
+#define I915_PRIORITY_NEWCLIENT BIT(0)
+
struct i915_sched_attr {
/**
* @priority: execution and service priority
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