[PATCH] drm/i915/gvt: implement per-vm mmio switching optimization

[changbin.du at gmail.com]

From: Changbin Du <changbin.du at intel.com>

Commit ab9da627906a ("drm/i915: make context status notifier head be
per engine") gives us a chance to inspect every single request. Then
we can eliminate unnecessary mmio switching for same vGPU. We only
need mmio switching for different VMs (including host).

This patch introduced a new general API intel_gvt_switch_mmio() to
replace the old intel_gvt_load/restore_render_mmio(). This function
save the last ring id internally which will be used for next switch.

This optimization is very useful if only one guest has plenty of
workloads and the host is mostly idle. The best case is no mmio
switching will happen.

Signed-off-by: Changbin Du <changbin.du at intel.com>
Signed-off-by: Du, Changbin <changbin.du at intel.com>
---
 drivers/gpu/drm/i915/gvt/render.c    | 39 ++++++++++++++++++++++++++++++++++--
 drivers/gpu/drm/i915/gvt/render.h    |  4 ++--
 drivers/gpu/drm/i915/gvt/scheduler.c | 29 ++++++++++++++++++++-------
 drivers/gpu/drm/i915/gvt/scheduler.h |  2 ++
 4 files changed, 63 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/render.c b/drivers/gpu/drm/i915/gvt/render.c
index c6e7972..260ef83 100644
--- a/drivers/gpu/drm/i915/gvt/render.c
+++ b/drivers/gpu/drm/i915/gvt/render.c
@@ -260,7 +260,7 @@ static void restore_mocs(struct intel_vgpu *vgpu, int ring_id)
 
 #define CTX_CONTEXT_CONTROL_VAL	0x03
 
-void intel_gvt_load_render_mmio(struct intel_vgpu *vgpu, int ring_id)
+static void switch_mmio_to_vgpu(struct intel_vgpu *vgpu, int ring_id)
 {
 	struct drm_i915_private *dev_priv = vgpu->gvt->dev_priv;
 	struct render_mmio *mmio;
@@ -312,7 +312,7 @@ void intel_gvt_load_render_mmio(struct intel_vgpu *vgpu, int ring_id)
 	handle_tlb_pending_event(vgpu, ring_id);
 }
 
-void intel_gvt_restore_render_mmio(struct intel_vgpu *vgpu, int ring_id)
+static void switch_mmio_to_host(struct intel_vgpu *vgpu, int ring_id)
 {
 	struct drm_i915_private *dev_priv = vgpu->gvt->dev_priv;
 	struct render_mmio *mmio;
@@ -348,3 +348,38 @@ void intel_gvt_restore_render_mmio(struct intel_vgpu *vgpu, int ring_id)
 				mmio->value, v);
 	}
 }
+
+/**
+ * intel_gvt_switch_render_mmio - switch mmio context of specific engine
+ * @pre: the last vGPU that own the engine
+ * @next: the vGPU to switch to
+ * @ring_id: specify the engine
+ *
+ * If pre is null indicates that host own the engine. If next is null
+ * indicates that we are switching to host workload.
+ */
+void intel_gvt_switch_mmio(struct intel_vgpu *pre,
+			   struct intel_vgpu *next, int ring_id)
+{
+
+	static enum intel_engine_id last_ring = -1;
+
+	if (WARN_ON((!pre && !next) || (pre && last_ring == -1)))
+		return;
+
+	gvt_dbg_render("switch mmio from %s to %s, last_ring %d, cur_ring %d\n",
+		       pre ? "vGPU" : "host", next ? "vGPU" : "HOST",
+		       last_ring, ring_id);
+
+	/**
+	 * TODO: Optimize for vGPU to vGPU switch by merging
+	 * switch_mmio_to_host() and switch_mmio_to_vgpu().
+	 */
+	if (pre)
+		switch_mmio_to_host(pre, last_ring);
+
+	if (next) {
+		switch_mmio_to_vgpu(next, ring_id);
+		last_ring = ring_id;
+	}
+}
diff --git a/drivers/gpu/drm/i915/gvt/render.h b/drivers/gpu/drm/i915/gvt/render.h
index dac1a3c..91db1d3 100644
--- a/drivers/gpu/drm/i915/gvt/render.h
+++ b/drivers/gpu/drm/i915/gvt/render.h
@@ -36,8 +36,8 @@
 #ifndef __GVT_RENDER_H__
 #define __GVT_RENDER_H__
 
-void intel_gvt_load_render_mmio(struct intel_vgpu *vgpu, int ring_id);
+void intel_gvt_switch_mmio(struct intel_vgpu *pre,
+			   struct intel_vgpu *next, int ring_id);
 
-void intel_gvt_restore_render_mmio(struct intel_vgpu *vgpu, int ring_id);
 
 #endif
diff --git a/drivers/gpu/drm/i915/gvt/scheduler.c b/drivers/gpu/drm/i915/gvt/scheduler.c
index bada32b..1caabea 100644
--- a/drivers/gpu/drm/i915/gvt/scheduler.c
+++ b/drivers/gpu/drm/i915/gvt/scheduler.c
@@ -139,21 +139,36 @@ static int shadow_context_status_change(struct notifier_block *nb,
 	struct intel_gvt *gvt = container_of(nb, struct intel_gvt,
 				shadow_ctx_notifier_block[req->engine->id]);
 	struct intel_gvt_workload_scheduler *scheduler = &gvt->scheduler;
-	struct intel_vgpu_workload *workload =
-		scheduler->current_workload[req->engine->id];
+	struct intel_vgpu_workload *workload;
+
+	if (!is_gvt_request(req)) {
+		if (action == INTEL_CONTEXT_SCHEDULE_IN && scheduler->last_vgpu) {
+			/* Switch from vGPU to host. */
+			intel_gvt_switch_mmio(scheduler->last_vgpu, NULL,
+					      req->engine->id);
+		}
+
+		scheduler->last_vgpu = NULL;
+		return NOTIFY_OK;
+	}
 
-	if (!is_gvt_request(req) || unlikely(!workload))
+	workload = scheduler->current_workload[req->engine->id];
+	if (unlikely(!workload))
 		return NOTIFY_OK;
 
 	switch (action) {
 	case INTEL_CONTEXT_SCHEDULE_IN:
-		intel_gvt_load_render_mmio(workload->vgpu,
-					   workload->ring_id);
+		if (scheduler->last_vgpu != workload->vgpu) {
+			/* Switch from host to vGPU or from vGPU to vGPU. */
+			intel_gvt_switch_mmio(scheduler->last_vgpu,
+					      workload->vgpu,
+					      req->engine->id);
+		}
+
 		atomic_set(&workload->shadow_ctx_active, 1);
+		scheduler->last_vgpu = workload->vgpu;
 		break;
 	case INTEL_CONTEXT_SCHEDULE_OUT:
-		intel_gvt_restore_render_mmio(workload->vgpu,
-					      workload->ring_id);
 		/* If the status is -EINPROGRESS means this workload
 		 * doesn't meet any issue during dispatching so when
 		 * get the SCHEDULE_OUT set the status to be zero for
diff --git a/drivers/gpu/drm/i915/gvt/scheduler.h b/drivers/gpu/drm/i915/gvt/scheduler.h
index 2cd725c..8a06cd9 100644
--- a/drivers/gpu/drm/i915/gvt/scheduler.h
+++ b/drivers/gpu/drm/i915/gvt/scheduler.h
@@ -38,6 +38,8 @@
 
 struct intel_gvt_workload_scheduler {
 	struct intel_vgpu *current_vgpu;
+	/* last_vgpu can be null when running i915 context */
+	struct intel_vgpu *last_vgpu;
 	struct intel_vgpu *next_vgpu;
 	struct intel_vgpu_workload *current_workload[I915_NUM_ENGINES];
 	bool need_reschedule;
-- 
2.7.4