linux-kernel - Re: [PATCH] cpuidle: reinitialize power_usage values when adding/removing C-states

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Date:	Thu, 18 Oct 2012 10:21:52 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Julius Werner <jwerner@...omium.org>
CC:	linux-kernel@...r.kernel.org, len.brown@...el.com, khilman@...com,
	rjw@...k.pl, deepthi@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
	g.trinabh@...il.com, snanda@...omium.org,
	Lists Linaro-dev <linaro-dev@...ts.linaro.org>
Subject: Re: [PATCH] cpuidle: reinitialize power_usage values when adding/removing
 C-states

On 10/17/2012 08:43 PM, Julius Werner wrote:
>> This is specific to the acpi and should be handled in the
>> processor_idle.c file instead of the cpuidle core code.
>>
>> Could be the function 'acpi_processor_cst_has_changed' the right place
>> to set a dummy power value for the power in the new C-state ?
> 
> Thanks for your feedback. I think it wouldn't be wise to split the
> dummy power value logic over two places, but I could submit a patch
> that makes set_power_states globally accessible and calls it from
> acpi_processor_cst_has_changed instead.

No please, do not export this function. That will add more confusion on
the acpi code and more generally in the cpuidle core code.

IIUC, a new state is inserted/deleted and we will set the entire array
of states to setup the power.

You have the acpi_processor_cst_has_changed function calling the
acpi_processor_setup_cpuidle_states function. It seems to be a good
candidate to setup the power of the new state. All the states are filled
again AFAICS under the lock.

> However, I do not think this should really be ACPI specific. It
> applies to any cpuidle driver that wants to change its idle states at
> runtime. Currently only the ACPI one does, but the future might bring
> others that would run into the same problem. I also think that
> set_power_states fits much better into cpuidle_enable_device
> conceptually anyway (right next to poll_idle_init which also does
> state initialization).

The states are now part of the cpuidle driver and the set_power_states
should remain to this file. The dynamic C-states brought some complexity
in the acpi code and honestly this code is very confusing.

Maybe one day, that would make sense but until then I am in favor of
keeping the arch specific bits in the drivers, especially when they are
*hum* so "complex".

poll_idle_init looks hackish for me and probably move it to the arch
would also make sense.

Thanks
  -- Daniel

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