[Intel-gfx] [PATCH v2 9/9] drm/i915/scheduler: Support user-defined priorities

[Chris Wilson]

Use a priority stored in the context as the initial value when
submitting a request. This allows us to change the default priority on a
per-context basis, allowing different contexts to be favoured with GPU
time at the expense of lower importance work. The user can adjust the
context's priority via I915_CONTEXT_PARAM_PRIORITY, with more positive
values being higher priority (they will be serviced earlier, after their
dependencies have been resolved). Any prerequisite work for an execbuf
will have its priority raised to match the new request as required.

Normal users can specify any value in the range of -1023 to 0 [default],
i.e. they can reduce the priority of their workloads (and temporarily
boost it back to normal if so desired).

Privileged users can specify any value in the range of -1023 to 1023,
[default is 0], i.e. they can raise their priority above all overs and
so potentially starve the system.

Note that the existing schedulers are not fair, nor load balancing, the
execution is strictly by priority on a first-come, first-served basis,
and the driver may choose to boost some requests above the range
available to users.

This priority was originally based around nice(2), but evolved to allow
clients to adjust their priority within a small range, and allow for a
privileged high priority range.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h         |  1 +
 drivers/gpu/drm/i915/i915_gem_context.c | 21 +++++++++++++++++++++
 drivers/gpu/drm/i915/i915_gem_request.c |  2 +-
 include/uapi/drm/i915_drm.h             |  3 +++
 4 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index e3b4412d0241..2da5ecad1f35 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -948,6 +948,7 @@ struct i915_gem_context {
 	/* Unique identifier for this context, used by the hw for tracking */
 	unsigned int hw_id;
 	u32 user_handle;
+	int priority; /* greater priorities are serviced first */
 
 	u32 ggtt_alignment;
 
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 34daef828dca..8df216eba490 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -476,6 +476,7 @@ int i915_gem_context_init(struct drm_device *dev)
 		return PTR_ERR(ctx);
 	}
 
+	ctx->priority = -I915_PRIORITY_MAX; /* lowest priority; idle task */
 	dev_priv->kernel_context = ctx;
 
 	DRM_DEBUG_DRIVER("%s context support initialized\n",
@@ -1095,6 +1096,9 @@ int i915_gem_context_getparam_ioctl(struct drm_device *dev, void *data,
 	case I915_CONTEXT_PARAM_NO_ERROR_CAPTURE:
 		args->value = !!(ctx->flags & CONTEXT_NO_ERROR_CAPTURE);
 		break;
+	case I915_CONTEXT_PARAM_PRIORITY:
+		args->value = ctx->priority;
+		break;
 	default:
 		ret = -EINVAL;
 		break;
@@ -1150,6 +1154,23 @@ int i915_gem_context_setparam_ioctl(struct drm_device *dev, void *data,
 				ctx->flags &= ~CONTEXT_NO_ERROR_CAPTURE;
 		}
 		break;
+
+	case I915_CONTEXT_PARAM_PRIORITY:
+		{
+			int priority = args->value;
+
+			if (args->size)
+				ret = -EINVAL;
+			else if (priority >= I915_PRIORITY_MAX ||
+				 priority <= -I915_PRIORITY_MAX)
+				ret = -EINVAL;
+			else if (priority > 0 && !capable(CAP_SYS_ADMIN))
+				ret = -EPERM;
+			else
+				ctx->priority = priority;
+		}
+		break;
+
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index fabd29fde175..4bfccb3d0c2c 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -844,7 +844,7 @@ void __i915_add_request(struct drm_i915_gem_request *request, bool flush_caches)
 	 * run at the earliest possible convenience.
 	 */
 	if (engine->schedule)
-		engine->schedule(request, 0);
+		engine->schedule(request, request->ctx->priority);
 
 	local_bh_disable();
 	i915_sw_fence_commit(&request->submit);
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index f51d429feaae..9fa5eee64f6b 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -404,6 +404,8 @@ typedef struct drm_i915_irq_wait {
 
 /* Query whether DRM_I915_GEM_EXECBUFFER2 supports user defined execution
  * priorities and the driver will attempt to execute batches in priority order.
+ * The initial priority for each batch is supplied by the context and is
+ * controlled via I915_CONTEXT_PARAM_PRIORITY.
  */
 #define I915_PARAM_HAS_SCHEDULER	 43
 
@@ -1283,6 +1285,7 @@ struct drm_i915_gem_context_param {
 #define I915_CONTEXT_PARAM_NO_ZEROMAP	0x2
 #define I915_CONTEXT_PARAM_GTT_SIZE	0x3
 #define I915_CONTEXT_PARAM_NO_ERROR_CAPTURE	0x4
+#define I915_CONTEXT_PARAM_PRIORITY	0x5
 	__u64 value;
 };
 
-- 
2.10.1