From: Valentin Schneider <valentin.schneider@arm.com>
To: Scott Wood <swood@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Rik van Riel <riel@surriel.com>, Mel Gorman <mgorman@suse.de>,
linux-kernel@vger.kernel.org,
linux-rt-users <linux-rt-users@vger.kernel.org>
Subject: Re: [RFC PATCH 1/3] sched/fair: Call newidle_balance() from finish_task_switch()
Date: Tue, 28 Apr 2020 22:37:18 +0100 [thread overview]
Message-ID: <jhjftcns35d.mognet@arm.com> (raw)
In-Reply-To: <20200428050242.17717-2-swood@redhat.com>
On 28/04/20 06:02, Scott Wood wrote:
> Thus, newidle_balance() is entered with interrupts enabled, which allows
> (in the next patch) enabling interrupts when the lock is dropped.
>
> Signed-off-by: Scott Wood <swood@redhat.com>
> ---
> kernel/sched/core.c | 7 ++++---
> kernel/sched/fair.c | 45 ++++++++++++++++----------------------------
> kernel/sched/sched.h | 6 ++----
> 3 files changed, 22 insertions(+), 36 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 9a2fbf98fd6f..0294beb8d16c 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3241,6 +3241,10 @@ static struct rq *finish_task_switch(struct task_struct *prev)
> }
>
> tick_nohz_task_switch();
> +
> + if (is_idle_task(current))
> + newidle_balance();
> +
This means we must go through a switch_to(idle) before figuring out we
could've switched to a CFS task, and do it then. I'm curious to see the
performance impact of that.
> return rq;
> }
>
> @@ -10425,14 +10408,23 @@ static inline void nohz_newidle_balance(struct rq *this_rq) { }
> * 0 - failed, no new tasks
> * > 0 - success, new (fair) tasks present
> */
> -int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
> +int newidle_balance(void)
> {
> unsigned long next_balance = jiffies + HZ;
> - int this_cpu = this_rq->cpu;
> + int this_cpu;
> struct sched_domain *sd;
> + struct rq *this_rq;
> int pulled_task = 0;
> u64 curr_cost = 0;
>
> + preempt_disable();
> + this_rq = this_rq();
> + this_cpu = this_rq->cpu;
> + local_bh_disable();
> + raw_spin_lock_irq(&this_rq->lock);
> +
> + update_rq_clock(this_rq);
> +
> update_misfit_status(NULL, this_rq);
I'm thinking this should be moved to where newidle_balance() used to be,
otherwise we have a window where the rq is flagged as having a misfit
task despite not having any runnable CFS tasks.
> /*
> * We must set idle_stamp _before_ calling idle_balance(), such that we
next prev parent reply other threads:[~2020-04-28 21:37 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-28 5:02 [RFC PATCH 0/3] newidle_balance() latency mitigation Scott Wood
2020-04-28 5:02 ` [RFC PATCH 1/3] sched/fair: Call newidle_balance() from finish_task_switch() Scott Wood
2020-04-28 21:37 ` Valentin Schneider [this message]
2020-04-28 22:09 ` Peter Zijlstra
2020-04-28 22:55 ` Scott Wood
2020-04-28 23:02 ` Peter Zijlstra
2020-04-28 23:20 ` Scott Wood
2020-04-29 9:05 ` Peter Zijlstra
2020-04-30 1:31 ` Scott Wood
2020-05-11 10:58 ` Peter Zijlstra
2020-05-11 12:13 ` Peter Zijlstra
2020-04-28 22:33 ` Scott Wood
2020-04-29 12:00 ` Valentin Schneider
2020-04-29 8:27 ` Vincent Guittot
2020-04-30 1:36 ` Scott Wood
2020-04-28 5:02 ` [RFC PATCH 2/3] sched/fair: Enable interrupts when dropping lock in newidle_balance() Scott Wood
2020-04-28 5:02 ` [RFC PATCH 3/3] sched,rt: break out of load balancing if an RT task appears Scott Wood
2020-04-28 21:56 ` Valentin Schneider
2020-04-28 22:33 ` Scott Wood
2020-04-28 22:52 ` Scott Wood
2020-04-29 12:01 ` Valentin Schneider
2020-04-28 13:27 ` [RFC PATCH 0/3] newidle_balance() latency mitigation Steven Rostedt
2020-04-29 23:13 ` Valentin Schneider
2020-04-30 7:44 ` Vincent Guittot
2020-04-30 10:14 ` Valentin Schneider
2020-04-30 12:42 ` Vincent Guittot
2020-04-30 13:56 ` Valentin Schneider
2020-04-30 12:48 ` Vincent Guittot
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