linux-kernel - Re: [PATCH v4 1/5] cpufreq: Don't wait for CPU to going offline to restart governor

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Message-ID: <53E93F86.5030304@codeaurora.org>
Date:	Mon, 11 Aug 2014 15:11:18 -0700
From:	Saravana Kannan <skannan@...eaurora.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Todd Poynor <toddpoynor@...gle.com>,
	"Srivatsa S . Bhat" <srivatsa@....edu>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH v4 1/5] cpufreq: Don't wait for CPU to going offline to
 restart governor

On 08/07/2014 01:54 AM, Viresh Kumar wrote:
> Sorry for the really long delay this time around. I am used to replying within a
> day normally, and this time it just took so much time.
>
> For next time please rebase on latest updates in pm/linux-next as there are
> few updates there.

Will do.

>
> On 25 July 2014 06:37, Saravana Kannan <skannan@...eaurora.org> wrote:
>> There's no need to wait for the CPU going down to fully go offline to
>> restart the governor. We can stop the governor, change policy->cpus and
>> immediately restart the governor. This should reduce the time without any
>> CPUfreq monitoring and also help future patches with simplifying the code.
>
> I agree with the idea here, though the $subject can be improved a bit
> here..

Suggestions welcome. I think the current one explains the main point of 
this change.

>> Signed-off-by: Saravana Kannan <skannan@...eaurora.org>
>> ---
>>   drivers/cpufreq/cpufreq.c | 33 ++++++++++++++++++---------------
>>   1 file changed, 18 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>> index 62259d2..ee0eb7b 100644
>> --- a/drivers/cpufreq/cpufreq.c
>> +++ b/drivers/cpufreq/cpufreq.c
>> @@ -1390,6 +1390,21 @@ static int __cpufreq_remove_dev_prepare(struct device *dev,
>>                  cpufreq_driver->stop_cpu(policy);
>>          }
>>
>> +       down_write(&policy->rwsem);
>> +       cpumask_clear_cpu(cpu, policy->cpus);
>> +       up_write(&policy->rwsem);
>
> There is a down_read() present early in this routine and we better update this
> at that place only.

I would rather not. My v1 patch series was super refactored to allow a 
lot of reuse, etc. But you guys complained about the diffs being 
confusing (which was a valid point).

Also, if we are talking about refactoring this, there's room for much 
better refactor at the end of the series. I will add a patch to the 
series to do the refactoring.

>
>> +       if (cpus > 1 && has_target()) {
>
> We already have a if (cpus > 1) block, move this there.

That only runs if cpu != policy->cpu. This needs to run irrespective of 
that.

>
>> +               ret = __cpufreq_governor(policy, CPUFREQ_GOV_START);
>> +               if (!ret)
>> +                       ret = __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);
>> +
>> +               if (ret) {
>> +                       pr_err("%s: Failed to start governor\n", __func__);
>> +                       return ret;
>> +               }
>> +       }
>> +
>>          return 0;
>>   }
>>
>> @@ -1410,15 +1425,12 @@ static int __cpufreq_remove_dev_finish(struct device *dev,
>>                  return -EINVAL;
>>          }
>>
>> -       down_write(&policy->rwsem);
>> +       down_read(&policy->rwsem);
>>          cpus = cpumask_weight(policy->cpus);
>> -
>> -       if (cpus > 1)
>> -               cpumask_clear_cpu(cpu, policy->cpus);
>> -       up_write(&policy->rwsem);
>> +       up_read(&policy->rwsem);
>>
>>          /* If cpu is last user of policy, free policy */
>> -       if (cpus == 1) {
>> +       if (cpus == 0) {
>>                  if (has_target()) {
>>                          ret = __cpufreq_governor(policy,
>>                                          CPUFREQ_GOV_POLICY_EXIT);
>> @@ -1447,15 +1459,6 @@ static int __cpufreq_remove_dev_finish(struct device *dev,
>>
>>                  if (!cpufreq_suspended)
>>                          cpufreq_policy_free(policy);
>> -       } else if (has_target()) {
>> -               ret = __cpufreq_governor(policy, CPUFREQ_GOV_START);
>> -               if (!ret)
>> -                       ret = __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);
>> -
>> -               if (ret) {
>> -                       pr_err("%s: Failed to start governor\n", __func__);
>> -                       return ret;
>> -               }
>>          }
>
> Also, you must mention in the log about an important change you are making.
> Don't know if there are any side effects...
>
> You are emptying policy->cpus on removal of last CPU of a policy, which wasn't
> the case earlier.

You mean the log in the cover letter? Will do.

-Saravana

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