From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: [PATCH] cpuidle - fix lock contention in the idle path Date: Sat, 29 Dec 2012 11:03:03 +0100 Message-ID: <50DEBFD7.5000104@linaro.org> References: <1356516108-11191-1-git-send-email-daniel.lezcano@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mail-ea0-f182.google.com ([209.85.215.182]:62855 "EHLO mail-ea0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751256Ab2L2KZY (ORCPT ); Sat, 29 Dec 2012 05:25:24 -0500 Received: by mail-ea0-f182.google.com with SMTP id a14so4703033eaa.13 for ; Sat, 29 Dec 2012 02:25:22 -0800 (PST) In-Reply-To: <1356516108-11191-1-git-send-email-daniel.lezcano@linaro.org> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: rafael.j.wysocki@intel.com, rja@sgi.com Cc: linux-pm@vger.kernel.org, pdeschrijver@nvidia.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org Hi Russ, Is it possible you try this patch on your 2048 cpus ? 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. >=20 > The problem is the contention with a large number of cpus because > they try to access the idle routine at the same time. >=20 > 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. >=20 > The cpuidle_unregister_driver function, leading the a NULL driver, > is not called before the cpuidle_unregister_device. >=20 > This is how is used the cpuidle api from the different drivers. >=20 > 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. >=20 > These modifications will need some code reorganization and rewrite > which does not fit with a fix. >=20 > The following patch is a hot fix by returning to the initial behavior > by removing the lock when getting the driver. >=20 > Signed-off-by: Daniel Lezcano > --- > drivers/cpuidle/driver.c | 8 +------- > 1 file changed, 1 insertion(+), 7 deletions(-) >=20 > 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; > =20 > - spin_lock(&cpuidle_driver_lock); > - drv =3D __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); > =20 >=20 --=20 Linaro.org =E2=94=82 Open source software for= ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog