2017-07-05 08:46:41

by Ganesh Mahendran

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: [email protected]
Signed-off-by: Ganesh Mahendran <[email protected]>
---
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

2017-07-05 11:59:27

by Peter Zijlstra

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: [email protected]
> Signed-off-by: Ganesh Mahendran <[email protected]>
> ---
> 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...

2017-07-06 01:39:58

by Ganesh Mahendran

Subject: Re: [PATCH] sched/fair: fix contribution calculation

Hello, Peter:

2017-07-05 19:59 GMT+08:00 Peter Zijlstra <[email protected]>:
> 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: [email protected]
>> Signed-off-by: Ganesh Mahendran <[email protected]>
>> ---
>> 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.