Re: [PATCH v2 4/7] sched/fair: Introduce sched_smt_siblings_idle()

From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>
Cc: 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>,
	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,
	"Tim C . Chen" <tim.c.chen@intel.com>
Subject: Re: [PATCH v2 4/7] sched/fair: Introduce sched_smt_siblings_idle()
Date: Tue, 6 Dec 2022 19:03:37 +0100	[thread overview]
Message-ID: <75ba5884-63c0-5180-00b8-e9764306a83e@arm.com> (raw)
In-Reply-To: <20221122203532.15013-5-ricardo.neri-calderon@linux.intel.com>

On 22/11/2022 21:35, Ricardo Neri wrote:
> Architectures that implement arch_asym_cpu_priority() may need to know the
> idle state of the SMT siblings of a CPU. The scheduler has this information
> and functionality. Expose it.
> 
> Move the existing functionality outside of the NUMA code.

[...]

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 0e4251f83807..9517c48df50e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1052,6 +1052,28 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
>   * Scheduling class queueing methods:
>   */
>  
> +static inline bool is_core_idle(int cpu)
> +{
> +#ifdef CONFIG_SCHED_SMT
> +	int sibling;
> +
> +	for_each_cpu(sibling, cpu_smt_mask(cpu)) {
> +		if (cpu == sibling)
> +			continue;
> +
> +		if (!idle_cpu(sibling))
> +			return false;
> +	}
> +#endif
> +
> +	return true;
> +}
> +
> +bool sched_smt_siblings_idle(int cpu)
> +{
> +	return is_core_idle(cpu);
> +}

Nitpick: Can we not just have one exported function for both use-cases:
NUMA and x86 ITMT?

[...]