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

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Message-ID: <CADAEsF-qK9pUC4YmTdJVdqTKzuc1O8toTJTJ=KE+07LU_nApcA@mail.gmail.com>
Date:   Thu, 6 Jul 2017 09:39:55 +0800
From:   Ganesh Mahendran <opensource.ganesh@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, mingo@...hat.com,
        stable@...r.kernel.org
Subject: Re: [PATCH] sched/fair: fix contribution calculation

Hello, Peter:

2017-07-05 19:59 GMT+08:00 Peter Zijlstra <peterz@...radead.org>:
> 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...

Yes, you are right. The latest kernel has fix this.
Do we need to fix this in LTS 4.1, 4.4?

Thanks.