Re: [PATCH 3/4] sched/fair: Consider SMT in ASYM_PACKING load balance

From: Peter Zijlstra <peterz@infradead.org>
To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
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: Tue, 6 Apr 2021 13:18:09 +0200	[thread overview]
Message-ID: <YGxDcccJ1U9ru0kV@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210406041108.7416-4-ricardo.neri-calderon@linux.intel.com>

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?

> +	return cpumask_equal(sched_group_span(sg), cpu_smt_mask(cpu));
> +#else
> +	return false;
> +#endif
> +}