From: grygorii.strashko@ti•com (Grygorii Strashko)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v2 7/7] ARM: smp: Add runtime PM support for CPU hotplug
Date: Fri, 4 Sep 2015 20:57:10 +0300 [thread overview]
Message-ID: <55E9DB76.3080904@ti.com> (raw)
In-Reply-To: <20150904151202.GA876@linaro.org>
Hi Lina,
On 09/04/2015 06:12 PM, Lina Iyer wrote:
> On Fri, Sep 04 2015 at 03:27 -0600, Russell King - ARM Linux wrote:
>> On Fri, Sep 04, 2015 at 10:17:35AM +0100, Russell King - ARM Linux wrote:
>>> On Thu, Sep 03, 2015 at 01:58:34PM -0600, Lina Iyer wrote:
>>> > @@ -401,6 +412,11 @@ asmlinkage void secondary_start_kernel(void)
>>> > local_irq_enable();
>>> > local_fiq_enable();
>>> >
>>> > + /* We are running, enable runtime PM for the CPU. */
>>> > + cpu_dev = get_cpu_device(cpu);
>>> > + if (cpu_dev)
>>> > + pm_runtime_get_sync(cpu_dev);
>>> > +
>>>
>>> Please no. This is fragile.
>>>
>>> pm_runtime_get_sync() can sleep, and this path is used when the system
>>> is fully up and running. Locks may be held, which cause this to sleep.
>>> However, we're calling it from a context where we can't sleep - which
>>> is the general rule for any part of system initialisation where we
>>> have not entered the idle thread yet (the idle thread is what we run
>>> when sleeping.)
>>>
> More explanation below.
>
> Another patch (3/7) in this series defines CPU devices as IRQ safe and
> therefore the dev->power.lock would be spinlock'd before calling the
> rest of the PM runtime code and the domain. The CPU PM domain would also
> be an IRQ safe domain (patch 2/7 makes the genpd framework usable in IRQ
> safe context).
There is one "small" problem with such approach :(
- It's incompatible with -RT kernel, because PM runtime can't be used
in atomic context on -RT. As result, CPU's hotplug will be broken
(CPUIdle will be broken also, but CPU hotplug is more important at least for me:).
Also, as for me, PM runtime + genpd is a little bit heavy-weight things
to be used for CPUIdle and It could affect on states with small wake-up latencies.
[...]
--
regards,
-grygorii
next prev parent reply other threads:[~2015-09-04 17:57 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-03 19:58 [PATCH v2 0/7] PM / Domains: Generic PM domains for CPUs/Clusters Lina Iyer
2015-09-03 19:58 ` [PATCH v2 1/7] PM / Domains: Allocate memory outside domain locks Lina Iyer
2015-09-03 19:58 ` [PATCH v2 2/7] PM / Domains: Support IRQ safe PM domains Lina Iyer
2015-09-04 10:02 ` Ulf Hansson
2015-09-04 16:05 ` Lina Iyer
2015-10-01 21:11 ` Geert Uytterhoeven
2015-09-03 19:58 ` [PATCH v2 3/7] drivers: cpu: Define CPU devices as IRQ safe Lina Iyer
2015-09-04 4:00 ` Stephen Boyd
2015-09-03 19:58 ` [PATCH v2 4/7] PM / Domains: Introduce PM domains for CPUs/clusters Lina Iyer
2015-09-04 3:54 ` Stephen Boyd
2015-09-03 19:58 ` [PATCH v2 5/7] ARM: cpuidle: Add runtime PM support for CPU idle Lina Iyer
2015-09-03 19:58 ` [PATCH v2 6/7] ARM64: smp: Add runtime PM support for CPU hotplug Lina Iyer
2015-09-30 12:36 ` Geert Uytterhoeven
2015-09-03 19:58 ` [PATCH v2 7/7] ARM: " Lina Iyer
2015-09-04 3:59 ` Stephen Boyd
2015-09-04 15:13 ` Lina Iyer
2015-09-04 7:39 ` Geert Uytterhoeven
2015-09-04 9:17 ` Russell King - ARM Linux
2015-09-04 9:27 ` Russell King - ARM Linux
2015-09-04 15:12 ` Lina Iyer
2015-09-04 16:23 ` Russell King - ARM Linux
2015-09-04 17:02 ` Lina Iyer
2015-09-04 17:46 ` Russell King - ARM Linux
2015-09-04 17:57 ` Grygorii Strashko [this message]
2015-09-04 18:45 ` Alan Stern
2015-09-04 21:46 ` Grygorii Strashko
2015-09-05 15:39 ` Alan Stern
2015-09-07 13:04 ` Rafael J. Wysocki
2015-09-07 13:37 ` Grygorii Strashko
2015-09-07 20:42 ` Rafael J. Wysocki
2015-09-08 8:21 ` Grygorii Strashko
2015-09-08 22:03 ` Kevin Hilman
2015-09-10 11:01 ` Grygorii Strashko
2015-09-22 17:32 ` Lina Iyer
2015-09-22 20:53 ` Thomas Gleixner
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