lkml.org 
[lkml]   [2012]   [Dec]   [31]   [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 Sat, Dec 29, 2012 at 11:03:03AM +0100, Daniel Lezcano wrote:
>
> Hi Russ,
>
> Is it possible you try this patch on your 2048 cpus ?

Yes, I will try it later today.
Thanks


> Thanks
>
> -- Daniel
>
> On 12/26/2012 11:01 AM, 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.
> >
> > The following patch is a hot fix by returning to the initial behavior
> > by removing the lock when getting the driver.
> >
> > Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> > ---
> > drivers/cpuidle/driver.c | 8 +-------
> > 1 file changed, 1 insertion(+), 7 deletions(-)
> >
> > diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
> > index 3af841f..c2b281a 100644
> > --- a/drivers/cpuidle/driver.c
> > +++ b/drivers/cpuidle/driver.c
> > @@ -235,16 +235,10 @@ EXPORT_SYMBOL_GPL(cpuidle_get_driver);
> > */
> > struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev)
> > {
> > - struct cpuidle_driver *drv;
> > -
> > if (!dev)
> > return NULL;
> >
> > - spin_lock(&cpuidle_driver_lock);
> > - drv = __cpuidle_get_cpu_driver(dev->cpu);
> > - spin_unlock(&cpuidle_driver_lock);
> > -
> > - return drv;
> > + return __cpuidle_get_cpu_driver(dev->cpu);
> > }
> > EXPORT_SYMBOL_GPL(cpuidle_get_cpu_driver);
> >
> >
>
>
> --
> <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

--
Russ Anderson, OS RAS/Partitioning Project Lead
SGI - Silicon Graphics Inc rja@sgi.com
--
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: 2012-12-31 16:41    [W:0.235 / U:0.528 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site