linux-kernel - Re: [PATCH v2 4/7] sched/fair: Introduce sched_smt_siblings

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Message-ID: <e55d091b-3d7a-6c4e-153b-b981b7e975bc@arm.com>
Date:   Thu, 22 Dec 2022 12:12:27 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ricardo Neri <ricardo.neri@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, "Tim C . Chen" <tim.c.chen@...el.com>
Subject: Re: [PATCH v2 4/7] sched/fair: Introduce sched_smt_siblings_idle()

On 12/12/2022 18:54, Ricardo Neri wrote:
> On Tue, Dec 06, 2022 at 07:03:37PM +0100, Dietmar Eggemann wrote:
>> On 22/11/2022 21:35, Ricardo Neri wrote:

[...]

>>> +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?
> 
> By adding a new function I intend to preserve the inlinig of is_core_idle()
> in update_numa_stats() (via numa_idle_core(), which is also inline). Do you
> think there is no value?

OK. It's only used in NUMA balancing (task_numa_fault() -> ... ->
update_numa_stats()). I can't see that this will have a noticeable perf
impact but only benchmark can really tell.

A `static inline bool sched_is_core_idle(int cpu)` via
include/linux/sched/topology.h might work? We have similar functions
(like sched_core_cookie_match()` but in the private scheduler header
file kernel/sched/sched.h though.

> A downside of having the new function is that now the code is duplicated
> in update_numa_stats() and sched_smt_siblings_idle().
> 
> I can take your suggestion if losing the inline is OK.

I doubt that it will have an impact but can't be sure.

[...]