From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>,
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>,
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 3/7] sched: Teach arch_asym_cpu_priority() the idle state of SMT siblings
Date: Wed, 21 Dec 2022 18:12:52 +0100 [thread overview]
Message-ID: <72ed59b5-c7e1-c425-d1b6-e8d703d11d7a@arm.com> (raw)
In-Reply-To: <20221212175433.GB27353@ranerica-svr.sc.intel.com>
On 12/12/2022 18:54, Ricardo Neri wrote:
> On Tue, Dec 06, 2022 at 06:54:39PM +0100, Dietmar Eggemann wrote:
>> On 22/11/2022 21:35, Ricardo Neri wrote:
[...]
>>> + * want to check the idle state of the SMT siblngs of @cpu.
>>
>> s/siblngs/siblings
>>
>> The scheduler calls sched_asym_prefer(..., true) from
>> find_busiest_queue(), asym_active_balance() and nohz_balancer_kick()
>
> In these places we are comparing two specific CPUs, of which the idle
> state of its siblings impact their throughput and, in consequence, the
> decision of attempt to balance load.
>
> In the places were sched_asym_prefer(...., false) is called we compare the
> destination CPU with a CPU that bears the priority of a sched group,
> regardless of the idle state of its siblings.
OK.
>> even from SMT layer on !x86.
>
> This is true, but the default arch_asym_cpu_priority ignores check_smt.
True.
>> So I guess a `bool check_smt` wouldn't be
>> sufficient to distinguish whether sched_smt_siblings_idle() should be
>> called or not.
>
> But it is the caller who determines whether the idle state of the SMT
> siblings of @cpu may be relevant.
I assume caller being the task scheduler here. Callers with
`check_smt=true` can be called from any SD level with SD_ASYM_PACKING.
Imagine an arch w/ SD_ASYM_PACKING on SMT & MC overwriting
arch_asym_cpu_priority(). `bool check_smt` wouldn't be sufficient to
know whether a call to something like sched_smt_siblings_idle()
(is_core_idle()) which iterates over cpu_smt_mask(cpu) would make sense.
>> To me this comment is a little bit misleading. Not an
>> issue currently since there is only the x86 overwrite right now.
>
> If my justification make sense to you, I can expand the comment to state
> that the caller decides whether check_smt is needed but arch-specific
> implementations are free to ignore it.
Not a big issue but to me if the task scheduler asks for `bool
check_smt` then archs would have to check to guarantee common behaviour.
And the meaning of `bool check_smt` on SMT is unclear to me.
Since only x86 would use this so far it can be adapted later for others
if needed.
[...]
next prev parent reply other threads:[~2022-12-21 17:14 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-22 20:35 [PATCH v2 0/7] x86/sched: Avoid unnecessary migrations within SMT domains Ricardo Neri
2022-11-22 20:35 ` [PATCH v2 1/7] sched/fair: Generalize asym_packing logic for SMT local sched group Ricardo Neri
2022-12-06 17:22 ` Dietmar Eggemann
2022-12-12 17:53 ` Ricardo Neri
2022-12-21 13:03 ` Dietmar Eggemann
2022-12-22 4:32 ` Ricardo Neri
2022-12-22 11:12 ` Dietmar Eggemann
2022-12-23 13:11 ` Ricardo Neri
2022-12-22 16:55 ` Valentin Schneider
2022-12-29 4:00 ` Ricardo Neri
2023-01-11 16:04 ` Valentin Schneider
2023-01-13 19:02 ` Ricardo Neri
2023-01-16 4:05 ` Ricardo Neri
2023-01-16 19:07 ` Valentin Schneider
2023-01-17 12:49 ` Ricardo Neri
2022-11-22 20:35 ` [PATCH v2 2/7] sched: Prepare sched_asym_prefer() to handle idle state of SMT siblings Ricardo Neri
2022-11-22 20:35 ` [PATCH v2 3/7] sched: Teach arch_asym_cpu_priority() the " Ricardo Neri
2022-12-06 17:54 ` Dietmar Eggemann
2022-12-12 17:54 ` Ricardo Neri
2022-12-21 17:12 ` Dietmar Eggemann [this message]
2022-12-22 4:55 ` Ricardo Neri
2022-12-22 16:56 ` Valentin Schneider
2022-11-22 20:35 ` [PATCH v2 4/7] sched/fair: Introduce sched_smt_siblings_idle() Ricardo Neri
2022-12-06 18:03 ` Dietmar Eggemann
2022-12-12 17:54 ` Ricardo Neri
2022-12-22 11:12 ` Dietmar Eggemann
2022-12-22 16:56 ` Valentin Schneider
2022-12-24 5:28 ` Ricardo Neri
2022-12-28 15:29 ` Chen Yu
2022-12-30 0:17 ` Ricardo Neri
2023-01-10 19:21 ` Valentin Schneider
2022-11-22 20:35 ` [PATCH v2 5/7] x86/sched: Remove SD_ASYM_PACKING from the "SMT" domain Ricardo Neri
2022-12-08 16:03 ` Ionela Voinescu
2022-12-14 16:59 ` Ricardo Neri
2022-12-15 16:48 ` Valentin Schneider
2022-12-20 0:42 ` Ricardo Neri
2022-12-22 16:56 ` Valentin Schneider
2022-12-29 19:02 ` Ricardo Neri
2023-01-10 19:17 ` Valentin Schneider
2023-01-13 1:31 ` Ricardo Neri
2022-11-22 20:35 ` [PATCH v2 6/7] x86/sched/itmt: Give all SMT siblings of a core the same priority Ricardo Neri
2022-11-22 20:35 ` [PATCH v2 7/7] x86/sched/itmt: Consider the idle state of SMT siblings Ricardo Neri
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