From: Peter Zijlstra <peterz@infradead.org>
To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Ricardo Neri <ricardo.neri@intel.com>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Ben Segall <bsegall@google.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Len Brown <len.brown@intel.com>, Mel Gorman <mgorman@suse.de>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
Steven Rostedt <rostedt@goodmis.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Valentin Schneider <vschneid@redhat.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/4] sched/fair: Avoid unnecessary migrations within SMT domains
Date: Tue, 18 Oct 2022 11:40:11 +0200 [thread overview]
Message-ID: <Y050e5XQkaUrwr5j@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20221018023527.GB23064@ranerica-svr.sc.intel.com>
On Mon, Oct 17, 2022 at 07:35:27PM -0700, Ricardo Neri wrote:
> On Thu, Aug 25, 2022 at 03:55:25PM -0700, Ricardo Neri wrote:
> > Intel processors that support Intel Turbo Boost Max 3.0 use asym_packing
> > to assign higher priorities to CPUs with higher maximum frequencies. It
> > artificially assigns, however, a lower priority to the higher-numbered
> > SMT siblings to ensure that they are used last.
> >
> > This results in unnecessary task migrations within the SMT domains.
> >
> > On processors with a mixture of higher-frequency SMT cores and lower-
> > frequency non-SMT cores (such as Intel hybrid processors), a lower-
> > priority CPU pulls tasks from the higher-priority cores if more than one
> > SMT sibling is busy.
> >
> > Do not use different priorities for each SMT sibling. Instead, tweak the
> > asym_packing load balancer to recognize SMT cores with more than one
> > busy sibling and let lower-priority CPUs pull tasks.
> >
> > Removing these artificial priorities avoids superfluous migrations and
> > lets lower-priority cores inspect all SMT siblings for the busiest queue.
>
> Hello. I'd like to know if there are any comments on these patches. This
> patchset is a requisite for the IPC classes of tasks patchset [1].
Urgh.. so I'm not liking this, afaict you're sprinkling SMT2
assumptions.
Why can't we make arch_asym_cpu_priority() depend on CPU state? Doesn't
it then magically work?
next prev parent reply other threads:[~2022-10-18 9:40 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-25 22:55 [PATCH 0/4] sched/fair: Avoid unnecessary migrations within SMT domains Ricardo Neri
2022-08-25 22:55 ` [PATCH 1/4] sched/fair: Simplify asym_packing logic for SMT sched groups Ricardo Neri
2022-10-18 9:34 ` Peter Zijlstra
2022-10-20 1:25 ` Ricardo Neri
2022-08-25 22:55 ` [PATCH 2/4] sched/fair: Do not disqualify either runqueues of " Ricardo Neri
2022-08-25 22:55 ` [PATCH 3/4] sched/fair: Let lower-priority CPUs do active balancing Ricardo Neri
2022-08-25 22:55 ` [PATCH 4/4] x86/sched: Avoid unnecessary migrations within SMT domains Ricardo Neri
2022-10-18 2:35 ` [PATCH 0/4] sched/fair: " Ricardo Neri
2022-10-18 9:40 ` Peter Zijlstra [this message]
2022-10-20 1:38 ` Ricardo Neri
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