linux-kernel - Re: [PATCH v4 0/2] cpufreq: cpufreq_driver

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Date:	Wed, 13 Mar 2013 15:50:41 -0500
From:	Nathan Zimmer <nzimmer@....com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	<viresh.kumar@...aro.org>, <cpufreq@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 0/2] cpufreq: cpufreq_driver_lock is hot on large systems

On 03/11/2013 06:23 PM, Rafael J. Wysocki wrote:
> On Friday, February 22, 2013 10:24:33 AM Nathan Zimmer wrote:
>> I am noticing the cpufreq_driver_lock is quite hot.
>> On an idle 512 system perf shows me most of the system time is spent on this
>> lock.  This is quite significant as top shows 5% of time in system time.
>> My solution was to first convert the lock to a rwlock and then to the rcu.
>>
>> v2: Rebase
>>
>> v3: Read the RCU documentation instead of skimming it.  Also I based on
>> git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git pm+acpi-3.9-rc1
>> I assumed that was what you would prefer Rafael.
>>
>> v4: Removed an unnecessary syncronize_rcu().
>>
>>
>> Nathan Zimmer (2):
>>    cpufreq: Convert the cpufreq_driver_lock to a rwlock
>>    cpufreq: Convert the cpufreq_driver_lock to use the rcu
>>
>>   drivers/cpufreq/cpufreq.c | 286 ++++++++++++++++++++++++++++++++++------------
>>   1 file changed, 211 insertions(+), 75 deletions(-)
> I'm going to take patch [1/2] for v3.10, but patch [2/2] still needs some
> work it seems.  Is that correct?  If so, are you going to send an update?
>
> Rafael
>

Viresh pointed out that cpufreq_cpu_data still needs a lock.
This means placing a vanilla spinlock back into __cpufreq_cpu_get which 
is what I need to avoid.  I haven't had the time I should to sort that out.


Nate


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