[PATCH v2 1/2] drm/i915/gvt: optimization of context shadowing

[Yan Zhao]

if the newly submitted guest context is the same as last shadowed one,
no need to copy them from guest again.

Currently using lrca + ring_context_gpa to identify whether two guest
contexts are the same.

The reason of why context id is not included is that it's recently
changed by i915 that it just increase the value indiscriminately if i915
perf is not on.
If i915 perf is on, I checked that the value is aligned with lrca.
so it's safe to omit context_id.

It also workes with old guest kernel like 4.20.

v2: rebased to 5.6.0-rc4+
Signed-off-by: Yan Zhao <yan.y.zhao at intel.com>
---
 drivers/gpu/drm/i915/gvt/gvt.h       |  4 ++++
 drivers/gpu/drm/i915/gvt/scheduler.c | 25 ++++++++++++++++++++-----
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/gvt.h b/drivers/gpu/drm/i915/gvt/gvt.h
index 58c2c7932e3f..e2d7ffd84457 100644
--- a/drivers/gpu/drm/i915/gvt/gvt.h
+++ b/drivers/gpu/drm/i915/gvt/gvt.h
@@ -163,6 +163,10 @@ struct intel_vgpu_submission {
 	const struct intel_vgpu_submission_ops *ops;
 	int virtual_submission_interface;
 	bool active;
+	struct {
+		u32 lrca;
+		u64 ring_context_gpa;
+	} last_ctx[I915_NUM_ENGINES];
 };
 
 struct intel_vgpu {
diff --git a/drivers/gpu/drm/i915/gvt/scheduler.c b/drivers/gpu/drm/i915/gvt/scheduler.c
index 1c95bf8cbed0..a66050a3d65a 100644
--- a/drivers/gpu/drm/i915/gvt/scheduler.c
+++ b/drivers/gpu/drm/i915/gvt/scheduler.c
@@ -134,7 +134,10 @@ static int populate_shadow_context(struct intel_vgpu_workload *workload)
 	struct page *page;
 	void *dst;
 	unsigned long context_gpa, context_page_num;
+	struct intel_vgpu_submission *s = &vgpu->submission;
 	int i;
+	bool skip = false;
+	int ring_id = workload->engine->id;
 
 	page = i915_gem_object_get_page(ctx_obj, LRC_STATE_PN);
 	shadow_ring_context = kmap(page);
@@ -171,12 +174,22 @@ static int populate_shadow_context(struct intel_vgpu_workload *workload)
 	sr_oa_regs(workload, (u32 *)shadow_ring_context, false);
 	kunmap(page);
 
-	if (IS_RESTORE_INHIBIT(shadow_ring_context->ctx_ctrl.val))
-		return 0;
+	gvt_dbg_sched("ring %s workload lrca %x, ctx_id %x, ctx gpa %llx",
+			workload->engine->name, workload->ctx_desc.lrca,
+			workload->ctx_desc.context_id,
+			workload->ring_context_gpa);
 
-	gvt_dbg_sched("ring %s workload lrca %x",
-		      workload->engine->name,
-		      workload->ctx_desc.lrca);
+	if ((s->last_ctx[ring_id].lrca ==
+				workload->ctx_desc.lrca) &&
+			(s->last_ctx[ring_id].ring_context_gpa ==
+				workload->ring_context_gpa))
+		skip = true;
+
+	s->last_ctx[ring_id].lrca = workload->ctx_desc.lrca;
+	s->last_ctx[ring_id].ring_context_gpa = workload->ring_context_gpa;
+
+	if (IS_RESTORE_INHIBIT(shadow_ring_context->ctx_ctrl.val) || skip)
+		return 0;
 
 	context_page_num = workload->engine->context_size;
 	context_page_num = context_page_num >> PAGE_SHIFT;
@@ -1260,6 +1273,8 @@ int intel_vgpu_setup_submission(struct intel_vgpu *vgpu)
 	atomic_set(&s->running_workload_num, 0);
 	bitmap_zero(s->tlb_handle_pending, I915_NUM_ENGINES);
 
+	memset(s->last_ctx, 0, sizeof(s->last_ctx));
+
 	i915_vm_put(&ppgtt->vm);
 	return 0;
 
-- 
2.17.1