linux-kernel - Re: [RFC PATCH V4 5/5] cpuidle: cpuidle driver for apm

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Date:	Wed, 23 Mar 2011 15:55:01 +0530
From:	Trinabh Gupta <trinabh@...ux.vnet.ibm.com>
To:	Stephen Rothwell <sfr@...b.auug.org.au>
CC:	arjan@...ux.intel.com, peterz@...radead.org, lenb@...nel.org,
	suresh.b.siddha@...el.com, benh@...nel.crashing.org,
	venki@...gle.com, ak@...ux.intel.com, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xensource.com
Subject: Re: [RFC PATCH V4 5/5] cpuidle: cpuidle driver for apm

Hi Stephen,

Thanks for reviewing.

On 03/23/2011 06:44 AM, Stephen Rothwell wrote:
> Hi,
>
> On Tue, 22 Mar 2011 18:03:40 +0530 Trinabh Gupta<trinabh@...ux.vnet.ibm.com>  wrote:
>>
>> +static int apm_setup_cpuidle(int cpu)
>> +{
>> +	struct cpuidle_device *dev = kzalloc(sizeof(struct cpuidle_device),
>> +					GFP_KERNEL);
>
> Same as xen comments: no NULL check.
>
>> +	int count = CPUIDLE_DRIVER_STATE_START;
>> +	dev->cpu = cpu;
>> +	dev->drv =&apm_idle_driver;
>
> Also wondering why you would ever have a different idle routine on
> different cpus?

Yes, this is an ongoing debate. Apparently it is a possibility
because of ACPI bugs. CPU's can have asymmetric C-states
and overall different idle routines on different cpus. Please
refer to http://lkml.org/lkml/2009/9/24/132 and
https://lkml.org/lkml/2011/2/10/37 for a discussion around this.

I have posted a patch series that does global registration
i.e same idle routines for each cpu. Please check
http://lkml.org/lkml/2011/3/22/161 . That series applies on
top of this series. Global registration significantly
simplifies the design, but still we are not sure about the
direction to take.

>
>> +
>> +	dev->states[count] = state_apm_idle;
>> +	count++;
>> +
>> +	dev->state_count = count;
>> +
>> +	if (cpuidle_register_device(dev))
>> +		return -EIO;
>
> And we leak dev.
>
>> +static void apm_idle_exit(void)
>> +{
>> +	cpuidle_unregister_driver(&apm_idle_driver);
>
> Do we leak the per cpu device structure here?

I will see how we can save
per cpu device structure pointers so that we can free them.

>
>> +	return;
>
> Unnecessary return statement.
>

Thanks,
-Trinabh
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