lkml.org 
[lkml]   [2013]   [Jan]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] cpuidle - fix lock contention in the idle path
On 01/02/2013 10:13 PM, Russ Anderson wrote:
> On Wed, Dec 26, 2012 at 11:01:48AM +0100, Daniel Lezcano wrote:
>> The commit bf4d1b5ddb78f86078ac6ae0415802d5f0c68f92 introduces
>> a lock in the cpuidle_get_cpu_driver function. This function
>> is used in the idle_call function.
>>
>> The problem is the contention with a large number of cpus because
>> they try to access the idle routine at the same time.
>>
>> The lock could be safely removed because of how is used the
>> cpuidle api. The cpuidle_register_driver is called first but
>> until the cpuidle_register_device is not called we don't
>> enter in the cpuidle idle call function because the device
>> is not enabled.
>>
>> The cpuidle_unregister_driver function, leading the a NULL driver,
>> is not called before the cpuidle_unregister_device.
>>
>> This is how is used the cpuidle api from the different drivers.
>>
>> However, a cleanup around the lock and a proper refcounting
>> mechanism should be used to ensure the consistency in the api,
>> like cpuidle_unregister_driver should failed if its refcounting
>> is not 0.
>>
>> These modifications will need some code reorganization and rewrite
>> which does not fit with a fix.
>
> I agree.
>
>> The following patch is a hot fix by returning to the initial behavior
>> by removing the lock when getting the driver.
>
> The patch fixes the problem. Verified on a system with 1024 cpus.
> Thanks.
>
>> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
>
> Reported-by: Russ Anderson <rja@sgi.com>
> Acked-by: Russ Anderson <rja@sgi.com>

Hi Rafael,

could you consider this patch for merging ?

Thanks
-- Daniel


--
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2013-01-04 08:41    [W:0.257 / U:5.380 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site