From: Mel Gorman <mgorman@suse.de>
To: Hao Jia <jiahao.os@bytedance.com>
Cc: mingo@redhat.com, peterz@infradead.org, mingo@kernel.org,
juri.lelli@redhat.com, vincent.guittot@linaro.org,
dietmar.eggemann@arm.com, rostedt@goodmis.org,
bsegall@google.com, bristot@redhat.com, vschneid@redhat.com,
mgorman@techsingularity.net, linux-kernel@vger.kernel.org
Subject: Re: [External] Re: [PATCH 1/2] sched/numa: Stop an exhastive search if an idle core is found
Date: Tue, 25 Oct 2022 10:32:26 +0100 [thread overview]
Message-ID: <20221025093226.dm4sjvdq2tofkwvc@suse.de> (raw)
In-Reply-To: <ced7c05a-121b-a77d-0c57-3e60abaecacd@bytedance.com>
On Tue, Oct 25, 2022 at 11:16:29AM +0800, Hao Jia wrote:
> > Remove the change in the first hunk and call break in the second hunk
> > after updating ns->idle_cpu.
> >
>
> Yes, thanks for your review.
> If I understand correctly, some things might look like this.
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e4a0b8bd941c..dfcb620bfe50 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1792,7 +1792,7 @@ static void update_numa_stats(struct task_numa_env
> *env,
> ns->nr_running += rq->cfs.h_nr_running;
> ns->compute_capacity += capacity_of(cpu);
>
> - if (find_idle && !rq->nr_running && idle_cpu(cpu)) {
> + if (find_idle && idle_core < 0 && !rq->nr_running &&
> idle_cpu(cpu)) {
> if (READ_ONCE(rq->numa_migrate_on) ||
> !cpumask_test_cpu(cpu, env->p->cpus_ptr))
> continue;
>
I meant more like the below but today I wondered why did I not do this in
the first place? The answer is because it's wrong and broken in concept.
The full loop is needed to calculate approximate NUMA stats at a
point in time. For example, the src and dst nr_running is needed by
task_numa_find_cpu. The search for an idle CPU or core in update_numa_stats
is simply taking advantage of the fact we are scanning anyway to keep
track of an idle CPU or core to avoid a second search as per ff7db0bf24db
("sched/numa: Prefer using an idle CPU as a migration target instead of
comparing tasks")
The patch I had in mind is below but that said, for both your version and
my initial suggestion
Naked-by: Mel Gorman <mgorman@suse.de>
For the record, this is what I was suggesting initially because it's more
efficient but it's wrong, don't do it.
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e4a0b8bd941c..7f1f6a1736a5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1800,7 +1800,12 @@ static void update_numa_stats(struct task_numa_env *env,
if (ns->idle_cpu == -1)
ns->idle_cpu = cpu;
+ /* If we find an idle core, stop searching. */
idle_core = numa_idle_core(idle_core, cpu);
+ if (idle_core >= 0) {
+ ns->idle_cpu = idle_core;
+ break;
+ }
}
}
rcu_read_unlock();
@@ -1808,9 +1813,6 @@ static void update_numa_stats(struct task_numa_env *env,
ns->weight = cpumask_weight(cpumask_of_node(nid));
ns->node_type = numa_classify(env->imbalance_pct, ns);
-
- if (idle_core >= 0)
- ns->idle_cpu = idle_core;
}
static void task_numa_assign(struct task_numa_env *env,
next prev parent reply other threads:[~2022-10-25 9:32 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-21 6:15 [PATCH 0/2] Optimize the process of scanning CPU for some functions Hao Jia
2022-10-21 6:15 ` [PATCH 1/2] sched/numa: Stop an exhastive search if an idle core is found Hao Jia
2022-10-24 13:34 ` Mel Gorman
2022-10-25 3:16 ` [External] " Hao Jia
2022-10-25 9:32 ` Mel Gorman [this message]
2022-10-25 11:10 ` Hao Jia
2022-10-25 13:32 ` Mel Gorman
2022-10-26 2:30 ` Hao Jia
2022-10-21 6:15 ` [PATCH 2/2] sched/core: Optimize the order of scanning CPU Hao Jia
2022-10-24 10:00 ` [PATCH 0/2] Optimize the process of scanning CPU for some functions Peter Zijlstra
2022-10-24 12:07 ` [External] " Hao Jia
2022-10-24 13:01 ` Hao Jia
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=20221025093226.dm4sjvdq2tofkwvc@suse.de \
--to=mgorman@suse.de \
--cc=bristot@redhat.com \
--cc=bsegall@google.com \
--cc=dietmar.eggemann@arm.com \
--cc=jiahao.os@bytedance.com \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@techsingularity.net \
--cc=mingo@kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=vincent.guittot@linaro.org \
--cc=vschneid@redhat.com \
/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).