drm/i915/gvt: Update time slice more frequently

When there is only one vGPU in GVT-g and it submits workloads
continuously, it will not be scheduled out, vgpu_update_timeslice
is not called and its sched_in_time is not updated in a long time,
which can be several seconds or longer.
Once GVT-g pauses to submit workload for this vGPU due to heavy
host CPU workload, this vGPU get scheduled out and
vgpu_update_timeslice is called, its left_ts will be subtract
by a big value from sched_out_time - sched_in_time.
When GVT-g is going to submit workload for this vGPU again,
it will not be scheduled in until gvt_balance_timeslice reaches
stage 0 and reset its left_ts, which introduces several
hunderand milliseconds latency.

This patch updates time slice in every ms to update sched_in_time
timely.

v2: revise commit message
v3: use more concise expr. (Zhenyu)
Signed-off-by: Zhipeng Gong <zhipeng.gong@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Min He <min.he@intel.com>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>

drivers/gpu/drm/i915/gvt/sched_policy.c

@@ -53,7 +53,6 @@ struct vgpu_sched_data {
 	bool active;
 
 	ktime_t sched_in_time;
-	ktime_t sched_out_time;
 	ktime_t sched_time;
 	ktime_t left_ts;
 	ktime_t allocated_ts;
@@ -69,15 +68,19 @@ struct gvt_sched_data {
 	ktime_t expire_time;
 };
 
-static void vgpu_update_timeslice(struct intel_vgpu *pre_vgpu)
+static void vgpu_update_timeslice(struct intel_vgpu *vgpu, ktime_t cur_time)
 {
 	ktime_t delta_ts;
-	struct vgpu_sched_data *vgpu_data = pre_vgpu->sched_data;
+	struct vgpu_sched_data *vgpu_data;
 
-	delta_ts = vgpu_data->sched_out_time - vgpu_data->sched_in_time;
+	if (!vgpu || vgpu == vgpu->gvt->idle_vgpu)
+		return;
 
-	vgpu_data->sched_time += delta_ts;
-	vgpu_data->left_ts -= delta_ts;
+	vgpu_data = vgpu->sched_data;
+	delta_ts = ktime_sub(cur_time, vgpu_data->sched_in_time);
+	vgpu_data->sched_time = ktime_add(vgpu_data->sched_time, delta_ts);
+	vgpu_data->left_ts = ktime_sub(vgpu_data->left_ts, delta_ts);
+	vgpu_data->sched_in_time = cur_time;
 }
 
 #define GVT_TS_BALANCE_PERIOD_MS 100
@@ -151,11 +154,7 @@ static void try_to_schedule_next_vgpu(struct intel_gvt *gvt)
 	}
 
 	cur_time = ktime_get();
-	if (scheduler->current_vgpu) {
-		vgpu_data = scheduler->current_vgpu->sched_data;
-		vgpu_data->sched_out_time = cur_time;
-		vgpu_update_timeslice(scheduler->current_vgpu);
-	}
+	vgpu_update_timeslice(scheduler->current_vgpu, cur_time);
 	vgpu_data = scheduler->next_vgpu->sched_data;
 	vgpu_data->sched_in_time = cur_time;
 
@@ -227,13 +226,13 @@ static void tbs_sched_func(struct gvt_sched_data *sched_data)
 void intel_gvt_schedule(struct intel_gvt *gvt)
 {
 	struct gvt_sched_data *sched_data = gvt->scheduler.sched_data;
+	ktime_t cur_time;
 
 	mutex_lock(&gvt->lock);
+	cur_time = ktime_get();
 
 	if (test_and_clear_bit(INTEL_GVT_REQUEST_SCHED,
 				(void *)&gvt->service_request)) {
-		ktime_t cur_time = ktime_get();
-
 		if (cur_time >= sched_data->expire_time) {
 			gvt_balance_timeslice(sched_data);
 			sched_data->expire_time = ktime_add_ms(
@@ -242,6 +241,7 @@ void intel_gvt_schedule(struct intel_gvt *gvt)
 	}
 	clear_bit(INTEL_GVT_REQUEST_EVENT_SCHED, (void *)&gvt->service_request);
 
+	vgpu_update_timeslice(gvt->scheduler.current_vgpu, cur_time);
 	tbs_sched_func(sched_data);
 
 	mutex_unlock(&gvt->lock);