From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.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.comi>, Mel Gorman <mgorman@suse.de>,
Len Brown <len.brown@intel.com>,
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
Aubrey Li <aubrey.li@linux.intel.com>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Ricardo Neri <ricardo.neri@intel.com>,
Quentin Perret <qperret@google.com>,
"Joel Fernandes (Google)" <joel@joelfernandes.org>,
linux-kernel@vger.kernel.org, Aubrey Li <aubrey.li@intel.com>,
Ben Segall <bsegall@google.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: [PATCH 3/4] sched/fair: Consider SMT in ASYM_PACKING load balance
Date: Thu, 8 Apr 2021 22:13:53 -0700 [thread overview]
Message-ID: <20210409051353.GB26235@ranerica-svr.sc.intel.com> (raw)
In-Reply-To: <YG7nMj8RxoyX9D3B@hirez.programming.kicks-ass.net>
On Thu, Apr 08, 2021 at 01:21:22PM +0200, Peter Zijlstra wrote:
> On Tue, Apr 06, 2021 at 04:17:51PM -0700, Ricardo Neri wrote:
> > On Tue, Apr 06, 2021 at 01:18:09PM +0200, Peter Zijlstra wrote:
> > > On Mon, Apr 05, 2021 at 09:11:07PM -0700, Ricardo Neri wrote:
> > > > +static bool cpu_group_is_smt(int cpu, struct sched_group *sg)
> > > > +{
> > > > +#ifdef CONFIG_SCHED_SMT
> > > > + if (!static_branch_likely(&sched_smt_present))
> > > > + return false;
> > > > +
> > > > + if (sg->group_weight == 1)
> > > > + return false;
> > > > +
> > > > + if (cpumask_weight(cpu_smt_mask(cpu)) == 1)
> > > > + return false;
> > >
> > > Please explain this condition. Why is it required?
> >
> > Thank you for your quick review Peter!
> >
> > Probably this is not required since the previous check verifies the
> > group weight, and the subsequent check makes sure that @sg matches the
> > SMT siblings of @cpu.
>
> So the thing is that cpumask_weight() can be fairly expensive, depending
> on how large the machine is.
>
> Now I suppose this mixing of SMT and !SMT cores is typical for 'small'
> machines (for now), but this is enabled for everything with ITMT on,
> which might very well include large systems.
>
> So yes, if it can go away, that'd be good.
Sure Peter, I think this check can be removed. I'll post a v2 with the
updates.
Thanks and BR,
Ricardo
next prev parent reply other threads:[~2021-04-09 5:14 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-06 4:11 [PATCH 0/4] sched/fair: Fix load balancing of SMT siblings with ASYM_PACKING Ricardo Neri
2021-04-06 4:11 ` [PATCH 1/4] sched/fair: Optimize checking for group_asym_packing Ricardo Neri
2021-04-06 4:11 ` [PATCH 2/4] sched/fair: Introduce arch_sched_asym_prefer_early() Ricardo Neri
2021-04-06 14:31 ` Vincent Guittot
2021-04-06 23:36 ` Ricardo Neri
2021-04-06 4:11 ` [PATCH 3/4] sched/fair: Consider SMT in ASYM_PACKING load balance Ricardo Neri
2021-04-06 11:17 ` Peter Zijlstra
2021-04-06 23:17 ` Ricardo Neri
2021-04-08 11:10 ` Peter Zijlstra
2021-04-09 5:12 ` Ricardo Neri
2021-04-06 11:18 ` Peter Zijlstra
2021-04-06 23:17 ` Ricardo Neri
2021-04-08 11:21 ` Peter Zijlstra
2021-04-09 5:13 ` Ricardo Neri [this message]
2021-04-06 4:11 ` [PATCH 4/4] x86/sched: Enable checks of the state of SMT siblings in load balancing Ricardo Neri
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