[RFC 1/1] drm/i915: Add scheduling priority to per-context parameters

[Dave Gordon <david.s.gordon@intel.com>]

The next use for the i915 get/set per-context parameters ioctl,
ahead of the introduction of the forthcoming GPU scheduler.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h         | 28 ++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_gem_context.c | 17 +++++++++++++++++
 include/uapi/drm/i915_drm.h             |  1 +
 3 files changed, 46 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 279e258..104b711 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -850,6 +850,33 @@ struct i915_ctx_hang_stats {
 	bool banned;
 };
 
+/*
+ * User-settable GFX scheduler priorities are on a scale of 1 (lowest
+ * priority) to 1023 (highest priority). The special value 0 means
+ * "let the system decide my priority automatically"; this is the
+ * default if the user process does not explicitly request a different
+ * priority. Any process may decrease its scheduling priority, but
+ * only a sufficiently-privileged process may increase it. However,
+ * it is always permissible to reset it to "system default", even if
+ * is currently lower than that. Thus, if the system-assigned default
+ * were, say, 256, a process could decrease it to 128, and then to 64.
+ * It could NOT then increase it to 128 again, but COULD request a
+ * priority of 0 -- which would actually reset it to 256, allowing
+ * the process to then request 128 again. (This avoids the issue with
+ * nice(2) priorities, namely that non-super-users can not increase
+ * scheduling priorities of their own processes, even if they were the
+ * ones that decreased the priorities in the first place).
+ */
+
+#define	i915_SCHED_PRIORITY_DEFAULT	0
+#define	i915_SCHED_PRIORITY_MIN		1
+#define	i915_SCHED_PRIORITY_MAX		1023
+
+struct i915_ctx_sched_info {
+	/* Scheduling priority */
+	unsigned long priority;
+};
+
 /* This must match up with the value previously used for execbuf2.rsvd1. */
 #define DEFAULT_CONTEXT_HANDLE 0
 
@@ -881,6 +908,7 @@ struct intel_context {
 	int flags;
 	struct drm_i915_file_private *file_priv;
 	struct i915_ctx_hang_stats hang_stats;
+	struct i915_ctx_sched_info sched_info;
 	struct i915_hw_ppgtt *ppgtt;
 
 	/* Legacy ring buffer submission */
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 74aa0c9..2728a0d 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -901,6 +901,9 @@ int i915_gem_context_getparam_ioctl(struct drm_device *dev, void *data,
 	case I915_CONTEXT_PARAM_NO_ZEROMAP:
 		args->value = ctx->flags & CONTEXT_NO_ZEROMAP;
 		break;
+	case I915_CONTEXT_PARAM_PRIORITY:
+		args->value = ctx->sched_info.priority;
+		break;
 	default:
 		ret = -EINVAL;
 		break;
@@ -938,6 +941,7 @@ int i915_gem_context_setparam_ioctl(struct drm_device *dev, void *data,
 		else
 			ctx->hang_stats.ban_period_seconds = args->value;
 		break;
+
 	case I915_CONTEXT_PARAM_NO_ZEROMAP:
 		if (args->size) {
 			ret = -EINVAL;
@@ -946,6 +950,19 @@ int i915_gem_context_setparam_ioctl(struct drm_device *dev, void *data,
 			ctx->flags |= args->value ? CONTEXT_NO_ZEROMAP : 0;
 		}
 		break;
+
+	case I915_CONTEXT_PARAM_PRIORITY:
+		if (args->size)
+			ret = -EINVAL;
+		else if (args->value > I915_SCHED_PRIORITY_MAX)
+			ret = -EINVAL;
+		else if (args->value > ctx->sched_info.priority &&
+			 !capable(CAP_SYS_ADMIN))
+			ret = -EPERM;
+		else
+			ctx->sched_info.priority = args->value;
+		break;
+
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index fd5aa47..a860263 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1126,6 +1126,7 @@ struct drm_i915_gem_context_param {
 	__u64 param;
 #define I915_CONTEXT_PARAM_BAN_PERIOD 0x1
 #define I915_CONTEXT_PARAM_NO_ZEROMAP 0x2
+#define I915_CONTEXT_PARAM_PRIORITY   0x3
 	__u64 value;
 };
 
-- 
1.9.1

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