From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Qi Zheng <arch0.zheng@gmail.com>,
mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
vincent.guittot@linaro.org, rostedt@goodmis.org,
bsegall@google.com, mgorman@suse.de
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched/fair: Fix the logic about active_balance in load_balance()
Date: Mon, 3 Aug 2020 09:36:55 +0200 [thread overview]
Message-ID: <c9afe264-d453-1676-77c9-b29db3481107@arm.com> (raw)
In-Reply-To: <20200802045141.130533-1-arch0.zheng@gmail.com>
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").
next prev parent reply other threads:[~2020-08-03 7:37 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
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 [this message]
2020-08-03 12:33 ` Qi Zheng
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