* [PATCH] sched/fair: Fix the logic about active_balance in load_balance()
@ 2020-08-02 4:51 Qi Zheng
2020-08-03 7:36 ` Dietmar Eggemann
0 siblings, 1 reply; 3+ messages in thread
From: Qi Zheng @ 2020-08-02 4:51 UTC (permalink / raw)
To: mingo, peterz, juri.lelli, vincent.guittot, dietmar.eggemann,
rostedt, bsegall, mgorman
Cc: linux-kernel, Qi Zheng
I think the unbalance scenario here should be that we need to
do active balance but it is not actually done. So fix it.
Signed-off-by: Qi Zheng <arch0.zheng@gmail.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 2ba8f230feb9..6d8c53718b67 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9710,7 +9710,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
} else
sd->nr_balance_failed = 0;
- if (likely(!active_balance) || voluntary_active_balance(&env)) {
+ if (likely(!active_balance) && voluntary_active_balance(&env)) {
/* We were unbalanced, so reset the balancing interval */
sd->balance_interval = sd->min_interval;
} else {
--
2.25.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] sched/fair: Fix the logic about active_balance in load_balance()
2020-08-02 4:51 [PATCH] sched/fair: Fix the logic about active_balance in load_balance() Qi Zheng
@ 2020-08-03 7:36 ` Dietmar Eggemann
2020-08-03 12:33 ` Qi Zheng
0 siblings, 1 reply; 3+ messages in thread
From: Dietmar Eggemann @ 2020-08-03 7:36 UTC (permalink / raw)
To: Qi Zheng, mingo, peterz, juri.lelli, vincent.guittot, rostedt,
bsegall, mgorman
Cc: linux-kernel
On 02/08/2020 06:51, Qi Zheng wrote:
> I think the unbalance scenario here should be that we need to
> do active balance but it is not actually done. So fix it.
>
> Signed-off-by: Qi Zheng <arch0.zheng@gmail.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 2ba8f230feb9..6d8c53718b67 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9710,7 +9710,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
> } else
> sd->nr_balance_failed = 0;
>
> - if (likely(!active_balance) || voluntary_active_balance(&env)) {
> + if (likely(!active_balance) && voluntary_active_balance(&env)) {
> /* We were unbalanced, so reset the balancing interval */
> sd->balance_interval = sd->min_interval;
> } else {
>
Active balance is potentially already been done when we reach this code.
See 'if (need_active_balance(&env))' and 'if (!busiest->active_balance)'
further up.
Here we only reset sd->balance_interval in case:
(A) the last load balance wasn't an active one
(B) the reason for the active load balance was:
(1) asym packing
(2) capacity of src_cpu is reduced compared to the one of dst_cpu
(3) misfit handling
(B) is done to not unnecessarily increase of balance interval, see
commit 46a745d90585 ("sched/fair: Fix unnecessary increase of balance
interval").
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] sched/fair: Fix the logic about active_balance in load_balance()
2020-08-03 7:36 ` Dietmar Eggemann
@ 2020-08-03 12:33 ` Qi Zheng
0 siblings, 0 replies; 3+ messages in thread
From: Qi Zheng @ 2020-08-03 12:33 UTC (permalink / raw)
To: Dietmar Eggemann, mingo, peterz, juri.lelli, vincent.guittot,
rostedt, bsegall, mgorman
Cc: linux-kernel
Hi Dietmar,
I understand, thank you for your review and very detailed explanation.
Yours,
Qi Zheng
On 2020/8/3 下午3:36, Dietmar Eggemann wrote:
> On 02/08/2020 06:51, Qi Zheng wrote:
>> I think the unbalance scenario here should be that we need to
>> do active balance but it is not actually done. So fix it.
>>
>> Signed-off-by: Qi Zheng <arch0.zheng@gmail.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 2ba8f230feb9..6d8c53718b67 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -9710,7 +9710,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
>> } else
>> sd->nr_balance_failed = 0;
>>
>> - if (likely(!active_balance) || voluntary_active_balance(&env)) {
>> + if (likely(!active_balance) && voluntary_active_balance(&env)) {
>> /* We were unbalanced, so reset the balancing interval */
>> sd->balance_interval = sd->min_interval;
>> } else {
>>
>
> Active balance is potentially already been done when we reach this code.
>
> See 'if (need_active_balance(&env))' and 'if (!busiest->active_balance)'
> further up.
>
> Here we only reset sd->balance_interval in case:
> (A) the last load balance wasn't an active one
> (B) the reason for the active load balance was:
> (1) asym packing
> (2) capacity of src_cpu is reduced compared to the one of dst_cpu
> (3) misfit handling
>
> (B) is done to not unnecessarily increase of balance interval, see
> commit 46a745d90585 ("sched/fair: Fix unnecessary increase of balance
> interval").
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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