From: Nicolas Pitre <nicolas.pitre@linaro.org>
To: "Brown, Len" <len.brown@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Preeti U Murthy <preeti@linux.vnet.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Preeti Murthy <preeti.lkml@gmail.com>,
"mingo@redhat.com" <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
LKML <linux-kernel@vger.kernel.org>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
Lists linaro-kernel <linaro-kernel@lists.linaro.org>
Subject: RE: [RFC PATCH 3/3] idle: store the idle state index in the struct rq
Date: Sat, 1 Feb 2014 15:13:59 -0500 (EST) [thread overview]
Message-ID: <alpine.LFD.2.11.1402011502070.2312@knanqh.ubzr> (raw)
In-Reply-To: <1A7043D5F58CCB44A599DFD55ED4C948452D3706@FMSMSX106.amr.corp.intel.com>
On Sat, 1 Feb 2014, Brown, Len wrote:
> > And your point is?
>
> It is a bad idea for an individual CPU to track the C-state
> of another CPU, which can change the cycle after it was checked.
Absolutely. And I'm far from advocating we do this either.
> We know it is a bad idea because we used to do it,
> until we realized code here can easily impact the
> performance critical path.
>
> In general, it is the OS's job to communicate constraints
> to the HW, and the HW to act on them. Not all HW is smart,
> so sometimes the OS has to do more hand-holding -- but
> less is more.
Less is more indeed. I'm certainly a big fan of that principle.
Just so you understand more about the context we need to care for on
ARM, I'd invite you to have a look at
Documentation/arm/cluster-pm-race-avoidance.txt.
I'm advocating we do _not_ track everything at the scheduler domain
simply because some cluster states are possible only if all the CPUs in
a cluster are idle, and that idleness is already tracked by the
scheduler at the scheduling domain level. So the information we don't
update can already be inferred indirectly and cheaply with the
information in place today.
Nicolas
next prev parent reply other threads:[~2014-02-01 20:14 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-30 14:09 [RFC PATCH 0/3] cpuidle/sched: move main idle function in the idle.c Daniel Lezcano
2014-01-30 14:09 ` [RFC PATCH 1/3] cpuidle: split cpuidle_idle_call main function into functions Daniel Lezcano
2014-01-30 15:27 ` Peter Zijlstra
2014-01-30 15:39 ` Daniel Lezcano
2014-01-30 19:39 ` Nicolas Pitre
2014-01-31 14:10 ` Daniel Lezcano
2014-01-30 14:09 ` [RFC PATCH 2/3] cpuidle: move the cpuidle_idle_call function to idle.c Daniel Lezcano
2014-01-30 19:42 ` Nicolas Pitre
2014-01-30 14:09 ` [RFC PATCH 3/3] idle: store the idle state index in the struct rq Daniel Lezcano
2014-01-30 15:31 ` Peter Zijlstra
2014-01-30 16:27 ` Daniel Lezcano
2014-01-30 16:35 ` Peter Zijlstra
2014-01-30 17:25 ` Daniel Lezcano
2014-01-30 17:50 ` Lorenzo Pieralisi
2014-01-30 21:02 ` Nicolas Pitre
2014-01-31 9:46 ` Vincent Guittot
2014-01-31 10:04 ` Lorenzo Pieralisi
2014-01-31 10:44 ` Daniel Lezcano
2014-01-31 8:45 ` Preeti Murthy
2014-01-31 9:02 ` Peter Zijlstra
2014-01-31 9:39 ` Preeti U Murthy
2014-01-31 10:24 ` Peter Zijlstra
2014-01-31 14:04 ` Daniel Lezcano
2014-01-31 14:12 ` Dietmar Eggemann
2014-01-31 15:07 ` Arjan van de Ven
2014-01-31 15:37 ` Daniel Lezcano
2014-01-31 15:50 ` Arjan van de Ven
2014-01-31 16:35 ` Daniel Lezcano
2014-01-31 16:42 ` Arjan van de Ven
2014-01-31 18:19 ` Nicolas Pitre
2014-02-01 6:00 ` Brown, Len
2014-02-01 15:31 ` Nicolas Pitre
2014-02-01 19:39 ` Brown, Len
2014-02-01 20:13 ` Nicolas Pitre [this message]
2014-02-01 15:40 ` Lorenzo Pieralisi
2014-02-03 12:54 ` Morten Rasmussen
2014-02-03 14:38 ` Arjan van de Ven
2014-02-03 14:56 ` Peter Zijlstra
2014-02-03 16:17 ` Arjan van de Ven
2014-02-11 16:41 ` Peter Zijlstra
2014-02-11 17:12 ` Arjan van de Ven
2014-02-11 19:47 ` Peter Zijlstra
2014-02-12 15:16 ` Lorenzo Pieralisi
2014-02-12 16:14 ` Arjan van de Ven
2014-02-12 17:37 ` Lorenzo Pieralisi
2014-02-12 19:05 ` Nicolas Pitre
2014-02-04 9:14 ` Ingo Molnar
2014-02-04 14:53 ` Arjan van de Ven
2014-02-04 14:56 ` Arjan van de Ven
2014-02-03 14:58 ` Nicolas Pitre
2014-01-31 10:15 ` Daniel Lezcano
2014-02-03 6:33 ` Preeti U Murthy
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