Messages in this thread | ![/](/images/icornerl.gif) | | From | Dietmar Eggemann <> | Subject | Re: [PATCH] sched/fair: Fix the logic about active_balance in load_balance() | Date | Mon, 3 Aug 2020 09:36:55 +0200 |
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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").
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