Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH] cpuidle - fix lock contention in the idle path | Date | Sat, 05 Jan 2013 01:03:11 +0100 |
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On Friday, January 04, 2013 07:27:24 AM Daniel Lezcano wrote: > 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 ?
Yes, I've taken it already.
I'll include it into the next pull request.
Thanks, Rafael
-- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.
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