From: Vincent Guittot <vincent.guittot@linaro.org>
To: Colin Cross <ccross@android.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>,
Kevin Hilman <khilman@ti.com>, Len Brown <len.brown@intel.com>,
linux-kernel@vger.kernel.org,
Amit Kucheria <amit.kucheria@linaro.org>,
linux-tegra@vger.kernel.org, linux-pm@lists.linux-foundation.org,
linux-omap@vger.kernel.org,
Arjan van de Ven <arjan@linux.intel.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [linux-pm] [PATCH 0/3] coupled cpuidle state support
Date: Fri, 27 Jan 2012 09:54:19 +0100 [thread overview]
Message-ID: <CAKfTPtAsO8z_8AnR8zSGZ9cm_7orDNxB3r09JAFk+2jdezUVmQ@mail.gmail.com> (raw)
In-Reply-To: <CAMbhsRTbVqV6p0py9NGZrpFPf2yvp-B0dr+o-m7qbdja_-Lfzw@mail.gmail.com>
On 20 January 2012 21:40, Colin Cross <ccross@android.com> wrote:
> On Fri, Jan 20, 2012 at 12:46 AM, Daniel Lezcano
> <daniel.lezcano@linaro.org> wrote:
>> Hi Colin,
>>
>> this patchset could be interesting to resolve in a generic way the cpu
>> dependencies.
>> What is the status of this patchset ?
>
> I can't do much with it right now, because I don't have any devices
> that can do SMP idle with a v3.2 kernel. I've started working on an
> updated version that avoids the spinlock, but it might be a while
> before I can test and post it. I'm mostly looking for feedback on the
> approach taken in this patch, and whether it will be useful for other
> SoCs besides Tegra and OMAP4.
>
Hi Colin,
In your patch, you put in safe state (WFI for most of platform) the
cpus that become idle and these cpus are woken up each time a new cpu
of the cluster becomes idle. Then, the cluster state is chosen and the
cpus enter the selected C-state. On ux500, we are using another
behavior for synchronizing the cpus. The cpus are prepared to enter
the c-state that has been chosen by the governor and the last cpu,
that enters idle, chooses the final cluster state (according to cpus'
C-state). The main advantage of this solution is that you don't need
to wake other cpus to enter the C-state of a cluster. This can be
quite worth full when tasks mainly run on one cpu. Have you also think
about such behavior when developing the coupled cpuidle driver ? It
could be interesting to add such behavior.
Regards,
Vincent
>> Did you have the opportunity to measure the power consumption with and
>> without this patchset ?
>
> Power consumption will be very dependent on the specific SoC in
> question. The most important factors are the power savings of the
> independent cpuidle state (normally WFI) vs. the hotplug state
> (normally 1 cpu in OFF), and the workload being tested.
>
> On a very idle system, these patches result in the same total power as
> hotplugging one cpu and letting the other idle normally. On a 25%
> busy system, you might see a slight increase in power, as the best
> independent cpuidle state might be WFI, vs 1 cpu in OFF mode in
> hotplug. On OMAP4, that difference is small, on the order of 10 mW.
> Once you hit the threshold where a hotplug governor would have
> hotplugged in the second cpu (lets say 40%), the savings from these
> patches are enormous, as you can hit the lowest power state up to 60%
> of the time, where the hotplug solution would never be going below WFI
> on both cpus. On OMAP4, that can be well over 100 mW.
> _______________________________________________
> linux-pm mailing list
> linux-pm@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/linux-pm
next prev parent reply other threads:[~2012-01-27 8:54 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-21 0:09 [PATCH 0/3] coupled cpuidle state support Colin Cross
2011-12-21 0:09 ` [PATCH 1/3] cpuidle: refactor out cpuidle_enter_state Colin Cross
2012-01-04 14:08 ` [linux-pm] " Jean Pihet
2011-12-21 0:09 ` [PATCH 2/3] cpuidle: fix error handling in __cpuidle_register_device Colin Cross
2011-12-21 0:09 ` [PATCH 3/3] cpuidle: add support for states that affect multiple cpus Colin Cross
2011-12-21 9:02 ` [PATCH 0/3] coupled cpuidle state support Arjan van de Ven
2011-12-21 9:40 ` Colin Cross
2011-12-21 9:44 ` Arjan van de Ven
2011-12-21 9:55 ` Colin Cross
2011-12-21 12:12 ` Arjan van de Ven
2011-12-21 19:05 ` Colin Cross
2011-12-21 19:36 ` Arjan van de Ven
2011-12-21 19:42 ` [linux-pm] " Colin Cross
2011-12-22 8:35 ` Shilimkar, Santosh
2011-12-22 8:53 ` Arjan van de Ven
2011-12-22 9:30 ` Shilimkar, Santosh
2011-12-22 21:20 ` Colin Cross
2012-03-14 0:39 ` Colin Cross
2012-01-04 0:41 ` Kevin Hilman
2012-01-04 17:27 ` Shilimkar, Santosh
2012-01-20 8:46 ` Daniel Lezcano
2012-01-20 20:40 ` Colin Cross
2012-01-25 14:04 ` Daniel Lezcano
2012-01-31 14:13 ` Daniel Lezcano
2012-01-27 8:54 ` Vincent Guittot [this message]
2012-01-27 17:32 ` [linux-pm] " Colin Cross
2012-02-01 12:13 ` Vincent Guittot
2012-02-01 14:59 ` Lorenzo Pieralisi
2012-02-01 17:30 ` Colin Cross
2012-02-01 18:07 ` Lorenzo Pieralisi
2012-02-03 1:19 ` Colin Cross
[not found] ` <8762e8kqi6.fsf@ti.com>
2012-03-14 0:28 ` Colin Cross
2012-03-14 0:47 ` Colin Cross
2012-03-14 14:23 ` [linux-pm] " Kevin Hilman
2012-03-14 2:04 ` Arjan van de Ven
2012-03-14 2:21 ` Colin Cross
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