From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH linux-next v8] cpufreq: convert the cpufreq_driver to use the rcu Date: Mon, 29 Apr 2013 14:37:28 -0700 Message-ID: <20130429213728.GR3780@linux.vnet.ibm.com> References: <515C5AB6.5090109@sgi.com> <1365087205-8708-1-git-send-email-nzimmer@sgi.com> <3218775.0Qs2EbHdzR@vostro.rjw.lan> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <3218775.0Qs2EbHdzR@vostro.rjw.lan> Sender: linux-pm-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Rafael J. Wysocki" Cc: Viresh Kumar , Nathan Zimmer , cpufreq@vger.kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org On Mon, Apr 29, 2013 at 12:22:32AM +0200, Rafael J. Wysocki wrote: > On Thursday, April 04, 2013 09:57:19 PM Viresh Kumar wrote: > > On 4 April 2013 20:23, Nathan Zimmer wrote: > > > We eventually would like to remove the rwlock cpufreq_driver_lock or convert > > > it back to a spinlock and protect the read sections with RCU. The first step in > > > that is moving the cpufreq_driver to use the rcu. > > > I don't see an easy wasy to protect the cpufreq_cpu_data structure with the > > > RCU, so I am leaving it with the rwlock for now since under certain configs > > > __cpufreq_cpu_get is hot spot with 256+ cores. > > > > > > v5: Go a different way and split up the lock and use the rcu > > > v6: use bools instead of checking function pointers > > > covert the cpufreq_data_lock to a rwlock > > > v7: Rebase to use the already accepted half > > > v8: Correct have_governor_per_policy > > > Reviewed location of rcu_read_(un)lock in several spots > > > > Sorry for long delay or too many versions of this patch :) > > > > Acked-by: Viresh Kumar > > Unfortunately, I had to revert this one, because it is obviously buggy. Why? > Because it adds rcu_read_lock()/rcu_read_unlock() around sysfs_create_file() > which may sleep due to a GFP_KERNEL memory allocation. Sorry for failing to > notice that earlier. One workaround might be to use SRCU, which allows sleeping in its critical sections. Thanx, Paul