Re: [PATCH v4 0/2] cpufreq: cpufreq_driver_lock is hot on large systems

[Nathan Zimmer]

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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