linux-kernel - [PATCH] sched/fair: fix contribution calculation

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Message-Id: <1499244390-4406-1-git-send-email-opensource.ganesh@gmail.com>
Date:   Wed,  5 Jul 2017 16:46:30 +0800
From:   Ganesh Mahendran <opensource.ganesh@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...hat.com, peterz@...radead.org, stable@...r.kernel.org,
        Ganesh Mahendran <opensource.ganesh@...il.com>
Subject: [PATCH] sched/fair: fix contribution calculation

Function __compute_runnable_contrib() is to calculate:
   \Sum 1024*y^n {for (1..n_period)}
But LOAD_AVG_MAX returns sum of 1024*y^n (0..n_period).
So we need to subtract 1024*y^0.

Cc: stable@...r.kernel.org
Signed-off-by: Ganesh Mahendran <opensource.ganesh@...il.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 90e26b1..777ad49 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2508,7 +2508,7 @@ static u32 __compute_runnable_contrib(u64 n)
 	if (likely(n <= LOAD_AVG_PERIOD))
 		return runnable_avg_yN_sum[n];
 	else if (unlikely(n >= LOAD_AVG_MAX_N))
-		return LOAD_AVG_MAX;
+		return LOAD_AVG_MAX - 1024;
 
 	/* Compute \Sum k^n combining precomputed values for k^i, \Sum k^j */
 	do {
-- 
1.9.1