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

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Message-ID: <20170705115915.GE4941@worktop>
Date:   Wed, 5 Jul 2017 13:59:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ganesh Mahendran <opensource.ganesh@...il.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        stable@...r.kernel.org
Subject: Re: [PATCH] sched/fair: fix contribution calculation

On Wed, Jul 05, 2017 at 04:46:30PM +0800, Ganesh Mahendran wrote:
> 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 {


This code no longer exists...