linux-kernel - Re: [PATCH 2/8] cpufreq: Fix misplaced call to cpufreq_update

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Date:	Mon, 15 Jul 2013 11:50:24 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	rjw@...k.pl, toralf.foerster@....de, robert.jarzmik@...el.com,
	durgadoss.r@...el.com, tianyu.lan@...el.com,
	lantianyu1986@...il.com, dirk.brandewie@...il.com,
	stern@...land.harvard.edu, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/8] cpufreq: Fix misplaced call to cpufreq_update_policy()

On 07/12/2013 12:36 PM, Viresh Kumar wrote:
> On 12 July 2013 03:45, Srivatsa S. Bhat
> <srivatsa.bhat@...ux.vnet.ibm.com> wrote:
>> The call to cpufreq_update_policy() is placed in the CPU hotplug callback
>> of cpufreq_stats, which has a higher priority than the CPU hotplug callback
>> of cpufreq-core. As a result, during CPU_ONLINE/CPU_ONLINE_FROZEN, we end up
>> calling cpufreq_update_policy() *before* calling cpufreq_add_dev() !
>> And for uninitialized CPUs, it just returns silently, not doing anything.
> 
> Hmm..
> 
>> To add to it, cpufreq_stats is not even the right place to call
>> cpufreq_update_policy() to begin with. The cpufreq core ought to handle
>> this in its own callback, from an elegance/relevance perspective.
>>
>> So move the invocation of cpufreq_update_policy() to cpufreq_cpu_callback,
>> and place it *after* cpufreq_add_dev().
>>
>> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
>> ---
>>
>>  drivers/cpufreq/cpufreq.c       |    1 +
>>  drivers/cpufreq/cpufreq_stats.c |    6 ------
>>  2 files changed, 1 insertion(+), 6 deletions(-)
>>
>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>> index ccc6eab..f8c3100 100644
>> --- a/drivers/cpufreq/cpufreq.c
>> +++ b/drivers/cpufreq/cpufreq.c
>> @@ -1943,6 +1943,7 @@ static int __cpuinit cpufreq_cpu_callback(struct notifier_block *nfb,
>>                 case CPU_ONLINE:
>>                 case CPU_ONLINE_FROZEN:
>>                         cpufreq_add_dev(dev, NULL);
>> +                       cpufreq_update_policy(cpu);
> 
> Do we need to call this for every hotplug of cpu? I am not
> talking about suspend/resume here.
> 

I don't think we need to, but I think it would be better to postpone
optimizations until all the cpufreq regressions get fixed. Later perhaps
we could revisit these minor optimizations if desired.

Regards,
Srivatsa S. Bhat

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