[Intel-gfx] [PATCH 11/11] drm/i915: Allow user control over preempt timeout on the important context

[Chris Wilson]

EGL_NV_realtime_priority?

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_context.c | 22 ++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_gem_context.h | 13 +++++++++++++
 drivers/gpu/drm/i915/i915_request.c     |  8 ++++++--
 drivers/gpu/drm/i915/intel_lrc.c        |  2 +-
 include/uapi/drm/i915_drm.h             | 12 ++++++++++++
 5 files changed, 54 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 5cfac0255758..dfb0a2b698c3 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -749,6 +749,15 @@ int i915_gem_context_getparam_ioctl(struct drm_device *dev, void *data,
 	case I915_CONTEXT_PARAM_PRIORITY:
 		args->value = ctx->priority;
 		break;
+	case I915_CONTEXT_PARAM_PREEMPT_TIMEOUT:
+		if (!(to_i915(dev)->caps.scheduler & I915_SCHEDULER_CAP_PREEMPTION))
+			ret = -ENODEV;
+		else if (args->size)
+			ret = -EINVAL;
+		else
+			args->value = ctx->preempt_timeout;
+		break;
+
 	default:
 		ret = -EINVAL;
 		break;
@@ -824,6 +833,19 @@ int i915_gem_context_setparam_ioctl(struct drm_device *dev, void *data,
 		}
 		break;
 
+	case I915_CONTEXT_PARAM_PREEMPT_TIMEOUT:
+		if (args->size)
+			ret = -EINVAL;
+		else if (args->value >= NSEC_PER_SEC)
+			ret = -EINVAL;
+		else if (!(to_i915(dev)->caps.scheduler & I915_SCHEDULER_CAP_PREEMPTION))
+			ret = -ENODEV;
+		else if (args->value && !capable(CAP_SYS_ADMIN))
+			ret = -EPERM;
+		else
+			ctx->preempt_timeout = args->value;
+		break;
+
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/drivers/gpu/drm/i915/i915_gem_context.h b/drivers/gpu/drm/i915/i915_gem_context.h
index 7854262ddfd9..74d4cadd729e 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.h
+++ b/drivers/gpu/drm/i915/i915_gem_context.h
@@ -150,6 +150,19 @@ struct i915_gem_context {
 	 */
 	int priority;
 
+	/**
+	 * @preempt_timeout: QoS guarantee for the high priority context
+	 *
+	 * Some clients need a guarantee that they will start executing
+	 * within a certain window, even at the expense of others. This entails
+	 * that if a preemption request is not honoured by the active context
+	 * within the timeout, we will reset the GPU to evict the hog and
+	 * run the high priority context instead.
+	 *
+	 * Timeout is stored in nanoseconds; exclusive max of 1s.
+	 */
+	u32 preempt_timeout;
+
 	/** ggtt_offset_bias: placement restriction for context objects */
 	u32 ggtt_offset_bias;
 
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 9d8dcebd9649..2cd4ea75d127 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -1101,8 +1101,12 @@ void __i915_request_add(struct i915_request *request, bool flush_caches)
 	 * run at the earliest possible convenience.
 	 */
 	rcu_read_lock();
-	if (engine->schedule)
-		engine->schedule(request, request->ctx->priority, 0);
+	if (engine->schedule) {
+		unsigned int timeout = request->ctx->preempt_timeout;
+		int priority = request->ctx->priority;
+
+		engine->schedule(request, priority, timeout);
+	}
 	rcu_read_unlock();
 
 	local_bh_disable();
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index e266657851e1..e782a621b40b 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1148,7 +1148,7 @@ static void execlists_submit_request(struct i915_request *request)
 	spin_lock_irqsave(&engine->timeline->lock, flags);
 
 	queue_request(engine, &request->priotree, rq_prio(request));
-	submit_queue(engine, rq_prio(request), 0);
+	submit_queue(engine, rq_prio(request), request->ctx->preempt_timeout);
 
 	GEM_BUG_ON(!engine->execlists.first);
 	GEM_BUG_ON(list_empty(&request->priotree.link));
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 7f5634ce8e88..6f10bbe90304 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1456,6 +1456,18 @@ struct drm_i915_gem_context_param {
 #define   I915_CONTEXT_MAX_USER_PRIORITY	1023 /* inclusive */
 #define   I915_CONTEXT_DEFAULT_PRIORITY		0
 #define   I915_CONTEXT_MIN_USER_PRIORITY	-1023 /* inclusive */
+
+/*
+ * I915_CONTEXT_PARAM_PREEMPT_TIMEOUT:
+ *
+ * Preemption timeout give in nanoseconds.
+ *
+ * Only allowed for privileged clients (CAP_SYS_ADMIN), this property allows
+ * the preempting context to kick out a GPU hog using a GPU reset if they do
+ * not honour the preemption request in time.
+ */
+#define I915_CONTEXT_PARAM_PREEMPT_TIMEOUT	0x7
+
 	__u64 value;
 };
 
-- 
2.16.3