Re: [PATCH 4/4] cpuidle - support multiple drivers

From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Peter De Schrijver <pdeschrijver@nvidia.com>
Cc: "rjw@sisk.pl" <rjw@sisk.pl>, "lenb@kernel.org" <lenb@kernel.org>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	"lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"patches@linaro.org" <patches@linaro.org>,
	"linaro-dev@lists.linaro.org" <linaro-dev@lists.linaro.org>
Subject: Re: [PATCH 4/4] cpuidle - support multiple drivers
Date: Thu, 04 Oct 2012 16:26:49 +0200	[thread overview]
Message-ID: <506D9CA9.8000308@linaro.org> (raw)
In-Reply-To: <20121004141425.GK13834@tbergstrom-lnx.Nvidia.com>

On 10/04/2012 04:14 PM, Peter De Schrijver wrote:
> On Tue, Sep 25, 2012 at 12:43:54AM +0200, Daniel Lezcano wrote:
>> With the tegra3 and the big.LITTLE [1] new architectures, several cpus
>> with different characteristics (latencies and states) can co-exists on the
>> system.
>>
>> The cpuidle framework has the limitation of handling only identical cpus.
>>
>> This patch removes this limitation by introducing the multiple driver support
>> for cpuidle.
>>
>> This option is configurable at compile time and should be enabled for the
>> architectures mentioned above. So there is no impact for the other platforms
>> if the option is disabled. The option defaults to 'n'. Note the multiple drivers
>> support is also compatible with the existing drivers, even if just one driver is
>> needed, all the cpu will be tied to this driver using an extra small chunk of
>> processor memory.
>>
>> The multiple driver support use a per-cpu driver pointer instead of a global
>> variable and the accessor to this variable are done from a cpu context.
>>
>> In order to keep the compatibility with the existing drivers, the function
>> 'cpuidle_register_driver' and 'cpuidle_unregister_driver' will register
>> the specified driver for all the cpus.
>>
>> The sysfs output for the 'current_driver' is changed when this option is
>> set by giving the drivers per cpu.
>>
>> eg.
>> cpu0: acpi_idle
>> cpu1: acpi_idle
>>
> 
> Is this allowed? I thought sysfs files can output only 1 line of data?

Ah yeah :)

Does it make sense to put the following files:

/sys/devices/system/cpu/cpu0/cpuidle/driver
 => acpi_idle
/sys/devices/system/cpu/cpu1/cpuidle/driver
 => acpi_idle

and the content of the file:

/sys/devices/system/cpu/cpuidle/current_driver will show the driver
associated with current cpu ?

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