From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: mingo@redhat.com, juri.lelli@redhat.com,
dietmar.eggemann@arm.com, rostedt@goodmis.org,
bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com
Subject: Re: [PATCH 2/2] sched/fair: Skip update_blocked_averages if we are defering load balance
Date: Tue, 5 Oct 2021 22:49:27 +0200 [thread overview]
Message-ID: <20211005204927.GE174703@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20211004171451.24090-3-vincent.guittot@linaro.org>
On Mon, Oct 04, 2021 at 07:14:51PM +0200, Vincent Guittot wrote:
> In newidle_balance(), the scheduler skips load balance to the new idle cpu
> when the 1st sd of this_rq is:
>
> this_rq->avg_idle < sd->max_newidle_lb_cost
>
> Doing a costly call to update_blocked_averages() will not be useful and
> simply adds overhead when this condition is true.
>
> Check the condition early in newidle_balance() to skip
> update_blocked_averages() when possible.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
> ---
> kernel/sched/fair.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1f78b2e3b71c..1294b78503d9 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10841,17 +10841,20 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
> */
> rq_unpin_lock(this_rq, rf);
>
> + rcu_read_lock();
> + sd = rcu_dereference_check_sched_domain(this_rq->sd);
> +
> if (this_rq->avg_idle < sysctl_sched_migration_cost ||
> - !READ_ONCE(this_rq->rd->overload)) {
> + !READ_ONCE(this_rq->rd->overload) ||
> + (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) {
set cino=(0:0, please.
Also, people have, in the past, tried to get rid of the first clause
here, perhaps this can replace it instead of augment it?
>
> - rcu_read_lock();
> - sd = rcu_dereference_check_sched_domain(this_rq->sd);
> if (sd)
> update_next_balance(sd, &next_balance);
> rcu_read_unlock();
>
> goto out;
> }
> + rcu_read_unlock();
There's another rcu_read_lock section right below this, at the very
least we can merge them.
Also, IIRC we're running all this with premption disabled, and since
rcu-sched got folded into rcu, all that rcu_read_*lock() stuff isn't
strictly required anymore.
(we're full circle there, back in the day RCU implied RCU-sched and the
scheduler relied on preempt-disable for lots of this stuff, then Paul
split them, and I spend a fair amount of time adding all this
rcu_read_*lock() crud, and now he's merge them again, and it can go
again).
Except of course, I think we need to make rcu_dereference_check happy
first :/
next prev parent reply other threads:[~2021-10-05 20:49 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-04 17:14 [PATCH 0/2] sched/fair: Improve cost accounting of newidle_balance Vincent Guittot
2021-10-04 17:14 ` [PATCH 1/2] sched/fair: account update_blocked_averages in newidle_balance cost Vincent Guittot
2021-10-05 20:40 ` Peter Zijlstra
2021-10-06 7:52 ` Vincent Guittot
2021-10-06 8:16 ` Vincent Guittot
2021-10-04 17:14 ` [PATCH 2/2] sched/fair: Skip update_blocked_averages if we are defering load balance Vincent Guittot
2021-10-05 20:49 ` Peter Zijlstra [this message]
2021-10-06 8:12 ` Vincent Guittot
2021-10-04 23:06 ` [PATCH 0/2] sched/fair: Improve cost accounting of newidle_balance Tim Chen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20211005204927.GE174703@worktop.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=bristot@redhat.com \
--cc=bsegall@google.com \
--cc=dietmar.eggemann@arm.com \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=mingo@redhat.com \
--cc=rostedt@goodmis.org \
--cc=tim.c.chen@linux.intel.com \
--cc=vincent.guittot@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).