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: Wed, 1 Feb 2012 13:13:26 +0100 [thread overview]
Message-ID: <CAKfTPtB3Kcy41H9g9u3u81kEHJeypi=GvOfOjcpdztzqN991nA@mail.gmail.com> (raw)
In-Reply-To: <CAMbhsRQYVXTZ2pX4mBrM6=SyGTqn_GY8xsW4rt_e21zerEzctA@mail.gmail.com>
Hi Colin,
Sorry for this late reply
On 27 January 2012 18:32, Colin Cross <ccross@android.com> wrote:
> On Fri, Jan 27, 2012 at 12:54 AM, Vincent Guittot
> <vincent.guittot@linaro.org> wrote:
>> 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.
>
> Waking up the cpus that are in the safe state is not done just to
> choose the target state, it's done to allow the cpus to take
> themselves to the target low power state. On ux500, are you saying
> you take the cpus directly from the safe state to a lower power state
> without ever going back to the active state? I once implemented Tegra
yes it is
> that way, and it required lots of nasty synchronization to prevent
> resetting the cpu at the same time that it was booting due to an
> interrupt, and I was later told that Tegra can't handle that sequence
> at all, although I haven't verified it yet.
you have to 2 main things to check :
- this cpu is the last one to enter an idle state
- other cpus are prepared to enter a cluster power state
- other cpus are in WFI
Vincent
>
> On platforms that can't turn the cpus off in a random order, or that
> can't take a cpu directly from the safe state to the target state,
> something like these coupled cpuidle patches are required. On
> platforms that can, the low power modes can be implemented without
> these patches, although it is very hard to do without race conditions.
next prev parent reply other threads:[~2012-02-01 12:13 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 ` [linux-pm] " Vincent Guittot
2012-01-27 17:32 ` Colin Cross
2012-02-01 12:13 ` Vincent Guittot [this message]
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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