[RFC PATCH] psi : calc psi memstall time more precisely

[Huangzhaoyang]

From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>

psi's memstall time is counted as simple as exit - entry so far, which ignore
the task's off cpu time. Fix it by calc the percentage of off time via task and
rq's util and runq load.

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
 kernel/sched/psi.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index cc25a3c..6812c7e 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -182,6 +182,8 @@ struct psi_group psi_system = {
 
 static void psi_avgs_work(struct work_struct *work);
 
+static unsigned long psi_memtime_fixup(u32 growth);
+
 static void group_init(struct psi_group *group)
 {
 	int cpu;
@@ -492,6 +494,23 @@ static u64 window_update(struct psi_window *win, u64 now, u64 value)
 	return growth;
 }
 
+static unsigned long psi_memtime_fixup(u32 growth)
+{
+	struct rq *rq = task_rq(current);
+	unsigned long growth_fixed = (unsigned long)growth;
+
+	if !(current->policy == SCHED_NORMAL || current->policy == SCHED_BATCH)
+		return growth_fixed;
+
+	if ((current->in_memstall)
+		&& (current->se.avg.util_avg <= rq->cfs.avg.util_avg)
+		&& current->se.avg.util_avg != 0)
+		growth_fixed = div64_ul((current->se.avg.util_avg + 1) * growth,
+			rq->cfs.avg.util_avg + rq->avg_rt.util_avg + 1);
+
+	return growth_fixed;
+}
+
 static void init_triggers(struct psi_group *group, u64 now)
 {
 	struct psi_trigger *t;
@@ -658,6 +677,7 @@ static void record_times(struct psi_group_cpu *groupc, u64 now)
 	}
 
 	if (groupc->state_mask & (1 << PSI_MEM_SOME)) {
+		delta = psi_memtime_fixup(delta);
 		groupc->times[PSI_MEM_SOME] += delta;
 		if (groupc->state_mask & (1 << PSI_MEM_FULL))
 			groupc->times[PSI_MEM_FULL] += delta;
@@ -928,8 +948,8 @@ void psi_memstall_leave(unsigned long *flags)
 	 */
 	rq = this_rq_lock_irq(&rf);
 
-	current->in_memstall = 0;
 	psi_task_change(current, TSK_MEMSTALL, 0);
+	current->in_memstall = 0;
 
 	rq_unlock_irq(rq, &rf);
 }
-- 
1.9.1