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.lezc...@linaro.org> > > Reported-by: Russ Anderson <r...@sgi.com> > Acked-by: Russ Anderson <r...@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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
