Re: [PATCH V3 11/13] cpufreq: governor: Keep list of policy_dbs within dbs_data
From: Rafael J. Wysocki
Date: Mon Feb 08 2016 - 08:35:16 EST
On Mon, Feb 8, 2016 at 2:30 PM, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> On 08-02-16, 14:21, Rafael J. Wysocki wrote:
>> On Mon, Feb 8, 2016 at 12:39 PM, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
>> > An instance of 'struct dbs_data' can support multiple 'struct
>> > policy_dbs_info' instances. To traverse all policy_dbs supported by a
>> > dbs_data, create a list of policy_dbs within dbs_data.
>> >
>> > Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
>>
>> Good idea overall, I like this.
>
> Thanks.
>
>> > ---
>> > drivers/cpufreq/cpufreq_governor.c | 12 ++++++++++++
>> > drivers/cpufreq/cpufreq_governor.h | 7 ++++++-
>> > 2 files changed, 18 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
>> > index ee3c2d92da53..e267acc67067 100644
>> > --- a/drivers/cpufreq/cpufreq_governor.c
>> > +++ b/drivers/cpufreq/cpufreq_governor.c
>> > @@ -489,6 +489,11 @@ static int cpufreq_governor_init(struct cpufreq_policy *policy)
>> > dbs_data->usage_count++;
>> > policy_dbs->dbs_data = dbs_data;
>> > policy->governor_data = policy_dbs;
>> > +
>> > + mutex_lock(&dbs_data->mutex);
>> > + list_add(&policy_dbs->list, &dbs_data->policy_dbs_list);
>> > + mutex_unlock(&dbs_data->mutex);
>>
>> The previous statements should be under the mutex too IMO, at least
>> the usage count incrementation in case two instances of this happen at
>> the same time.
>>
>> That can't happen now, but if we want to get rid of dbs_data_mutex
>> going forward, having it under the mutex will be actually useful.
>
> I think we should keep it precise for now. Right now, we are only
> concerned about the list modification, so just lock around that.
>
> Once we are going to remove dbs_data_mutex, then we can cover more
> things under it.
>
> Is there anything that is broken right now ?
Yes, the logic.
The counter technically is the number of items in policy_dbs_list.
Updating the list alone under the lock is simply illogical.
>> > +
>> > return 0;
>> > }
>> >
>> > @@ -500,8 +505,11 @@ static int cpufreq_governor_init(struct cpufreq_policy *policy)
>> >
>> > dbs_data->usage_count = 1;
>> > dbs_data->gov = gov;
>> > + INIT_LIST_HEAD(&dbs_data->policy_dbs_list);
>> > mutex_init(&dbs_data->mutex);
>> >
>> > + list_add(&policy_dbs->list, &dbs_data->policy_dbs_list);
>>
>> That line should go to where policy_dbs->dbs_data is set so it is
>> clear that they go together.
>
> Okay.
>
>> And I'd set the usage count to 1 in
>> there too for consistency.
>
> I am not sure about including any updates within the lock, which don't
> need protection in current state of code.
Well, if you're not sure, then please simply follow my request. :-)
Thanks,
Rafael