drm/i915/gt: Make timeslice duration configurable

Execlists uses a scheduling quantum (a timeslice) to alternate execution
between ready-to-run contexts of equal priority. This ensures that all
users (though only if they of equal importance) have the opportunity to
run and prevents livelocks where contexts may have implicit ordering due
to userspace semaphores. However, not all workloads necessarily benefit
from timeslicing and in the extreme some sysadmin may want to disable or
reduce the timeslicing granularity.

The timeslicing mechanism can be compiled out^W^W disabled (but should
DCE!) with

	./scripts/config --set-val DRM_I915_TIMESLICE_DURATION 0

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191029091632.26281-1-chris@chris-wilson.co.uk

1 files changed, 13 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
index 9507d750ae14..5e8c365548f0 100644
--- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
+++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
@@ -440,6 +440,8 @@ static int live_timeslice_preempt(void *arg)
 	 * need to preempt the current task and replace it with another
 	 * ready task.
 	 */
+	if (!IS_ACTIVE(CONFIG_DRM_I915_TIMESLICE_DURATION))
+		return 0;
 
 	obj = i915_gem_object_create_internal(gt->i915, PAGE_SIZE);
 	if (IS_ERR(obj))
@@ -514,6 +516,11 @@ static void wait_for_submit(struct intel_engine_cs *engine,
 	} while (!i915_request_is_active(rq));
 }
 
+static long timeslice_threshold(const struct intel_engine_cs *engine)
+{
+	return 2 * msecs_to_jiffies_timeout(timeslice(engine)) + 1;
+}
+
 static int live_timeslice_queue(void *arg)
 {
 	struct intel_gt *gt = arg;
@@ -531,6 +538,8 @@ static int live_timeslice_queue(void *arg)
 	 * ELSP[1] is already occupied, so must rely on timeslicing to
 	 * eject ELSP[0] in favour of the queue.)
 	 */
+	if (!IS_ACTIVE(CONFIG_DRM_I915_TIMESLICE_DURATION))
+		return 0;
 
 	obj = i915_gem_object_create_internal(gt->i915, PAGE_SIZE);
 	if (IS_ERR(obj))
@@ -608,8 +617,8 @@ static int live_timeslice_queue(void *arg)
 			err = -EINVAL;
 		}
 
-		/* Timeslice every jiffie, so within 2 we should signal */
-		if (i915_request_wait(rq, 0, 3) < 0) {
+		/* Timeslice every jiffy, so within 2 we should signal */
+		if (i915_request_wait(rq, 0, timeslice_threshold(engine)) < 0) {
 			struct drm_printer p =
 				drm_info_printer(gt->i915->drm.dev);
 
@@ -1383,7 +1392,7 @@ static int __cancel_hostile(struct live_preempt_cancel *arg)
 	int err;
 
 	/* Preempt cancel non-preemptible spinner in ELSP0 */
-	if (!CONFIG_DRM_I915_PREEMPT_TIMEOUT)
+	if (!IS_ACTIVE(CONFIG_DRM_I915_PREEMPT_TIMEOUT))
 		return 0;
 
 	GEM_TRACE("%s(%s)\n", __func__, arg->engine->name);
@@ -2030,7 +2039,7 @@ static int live_preempt_timeout(void *arg)
 	 * Check that we force preemption to occur by cancelling the previous
 	 * context if it refuses to yield the GPU.
 	 */
-	if (!CONFIG_DRM_I915_PREEMPT_TIMEOUT)
+	if (!IS_ACTIVE(CONFIG_DRM_I915_PREEMPT_TIMEOUT))
 		return 0;
 
 	if (!HAS_LOGICAL_RING_PREEMPTION(gt->i915))