linux-kernel - [PATCH v2] sched/pelt: Keep UTIL_AVG_UNCHANGED flag in sync when calculating last_enqueued

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Date:   Fri,  7 May 2021 19:20:31 +0800
From:   Xuewen Yan <xuewen.yan94@...il.com>
To:     vincent.donnefort@....com, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com
Cc:     rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, linux-kernel@...r.kernel.org,
        zhang.lyra@...il.com, xuewyan@...mail.com
Subject: [PATCH v2] sched/pelt: Keep UTIL_AVG_UNCHANGED flag in sync when calculating last_enqueued_diff

From: Xuewen Yan <xuewen.yan@...soc.com>

Last_enqueued_diff's meaning: "diff = util_est.enqueued(p) - task_util(p)".
When calculating last_enqueued_diff, we add UTIL_AVG_UNCHANGED flag, which
is the LSB, for task_util, but don't add the flag for util_est.enqueued.
However the enqueued's flag had been cleared when the task util changed.
As a result, we add +1 to the diff, this is therefore reducing slightly
UTIL_EST_MARGIN.

Add the flag for util_est.enqueued to have a accurate computation.

Fixes: b89997aa88f0b sched/pelt: Fix task util_est update filtering

Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e5e457fa9dc8..94d77b4fa601 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3996,7 +3996,7 @@ static inline void util_est_update(struct cfs_rq *cfs_rq,
 	if (ue.enqueued & UTIL_AVG_UNCHANGED)
 		return;
 
-	last_enqueued_diff = ue.enqueued;
+	last_enqueued_diff = (ue.enqueued | UTIL_AVG_UNCHANGED);
 
 	/*
 	 * Reset EWMA on utilization increases, the moving average is used only
-- 
2.29.0