From: Tejun Heo <tj@kernel.org>
To: Joel Fernandes <joelagnelf@nvidia.com>
Cc: linux-kernel@vger.kernel.org, David Vernet <void@manifault.com>,
Andrea Righi <arighi@nvidia.com>,
Changwoo Min <changwoo@igalia.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Valentin Schneider <vschneid@redhat.com>
Subject: Re: [PATCH RFC] sched_ext: Choose prev_cpu if idle and cache affine without WF_SYNC
Date: Mon, 17 Mar 2025 12:25:50 -1000 [thread overview]
Message-ID: <Z9ihbiUV7dohm7FT@slm.duckdns.org> (raw)
In-Reply-To: <b0dea973-bf41-4f44-850c-7bc860d5bf8a@nvidia.com>
Hello,
On Mon, Mar 17, 2025 at 11:07:36PM +0100, Joel Fernandes wrote:
...
> > I think it's preferring idle core a
> > bit too much - it probably doesn't make sense to cross the NUMA boundary if
> > there is an idle CPU in this node, at least.
>
> Yes, that is a bit extreme. I believe that is what my patch is fixing. If
> previous CPU and current CPU share cache, we prefer busy cores with free
> previous idle SMT, otherwise go looking for fully idle cores. But it sounds like
> from Peter's reply that is not necessarily a good thing to do in case 'fast
> numa'. So I guess there is no good answer (?) or way of doing it.
Yeah, recent AMD CPUs can be configured into NUMA mode where each chiplet is
reported as a node and they do behave like one as each has its own memory
connection but the distances among them are significantly closer than
traditional multi-socket. That said, I think the implementation is still a
bit too happy to jump the boundary. What Andrea is suggesting seems
reasonable?
Thanks.
--
tejun
next prev parent reply other threads:[~2025-03-17 22:25 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-17 8:28 [PATCH RFC] sched_ext: Choose prev_cpu if idle and cache affine without WF_SYNC Joel Fernandes
2025-03-17 17:08 ` Tejun Heo
2025-03-17 17:30 ` Andrea Righi
2025-03-17 17:44 ` Peter Zijlstra
2025-03-18 5:17 ` Andrea Righi
2025-03-17 22:11 ` Joel Fernandes
2025-03-18 5:09 ` Andrea Righi
2025-03-18 17:00 ` Joel Fernandes
2025-03-18 17:46 ` Andrea Righi
2025-03-18 22:37 ` Joel Fernandes
2025-03-17 22:07 ` Joel Fernandes
2025-03-17 22:25 ` Tejun Heo [this message]
2025-03-17 22:45 ` Joel Fernandes
2025-03-18 0:12 ` Libo Chen
2025-03-18 0:14 ` Tejun Heo
2025-03-17 17:20 ` Andrea Righi
2025-03-17 22:44 ` Joel Fernandes
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