Re: [PATCH V2 5/6] cpufreq: governor: replace per-cpu delayed work with timers

Viresh Kumar
2015-12-04T06:11:06Z

On 04-12-15, 02:18, Rafael J. Wysocki wrote:
> > + shared->skip_work--;
>
> Is there any reason for incrementing and decrementing this instead of setting
> it to either 0 or 1 (or maybe either 'true' or 'false' for that matter)?
>
> If my reading of the patch is correct, it can only be either 0 or 1 anyway, right?

No. It can be 0, 1 or 2.

If the timer handler is running on any CPU, we increment skip_work, so
its value is 1. If at the same time, we try to stop the governor, we
increment it again and its value is 2 now.

Once timer-handler finishes, it decrements it and its value become 1.
Which guarantees that no other timer handler starts executing at this
point of time and we can safely do gov_cancel_timers(). And once we
are sure that we don't have any work/timer left, we make it 0 (as we
aren't sure of the current value, which can be 0 (if the timer handler
wasn't running when we stopped the governor) or 1 (if the timer
handler was running while stopping the governor)).

Hope this clarifies it.

> > +static void dbs_timer_handler(unsigned long data)
> > +{
> > + struct cpu_dbs_info *cdbs = (struct cpu_dbs_info *)data;
> > + struct cpu_common_dbs_info *shared = cdbs->shared;
> > + struct cpufreq_policy *policy;
> > + unsigned long flags;
> > +
> > + spin_lock_irqsave(&shared->timer_lock, flags);
> > + policy = shared->policy;
>
> Why do we need policy here?
>
> > +
> > + /*
> > + * Timer handler isn't allowed to queue work at the moment, because:
> > + * - Another timer handler has done that
> > + * - We are stopping the governor
> > + * - Or we are updating the sampling rate of ondemand governor
> > + */
> > + if (shared->skip_work)
> > + goto unlock;
> > +
> > + shared->skip_work++;
> > + queue_work(system_wq, &shared->work);
> >
> > unlock:
>
> What about writing the above as
>
> if (!shared->work_in_progress) {
> shared->work_in_progress = true;
> queue_work(system_wq, &shared->work);
> }
>
> and then you won't need the unlock label.

Here is a diff for that:

diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index a3f9bc9b98e9..c9e420bd0eec 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -265,11 +265,9 @@ static void dbs_timer_handler(unsigned long data)
{
struct cpu_dbs_info *cdbs = (struct cpu_dbs_info *)data;
struct cpu_common_dbs_info *shared = cdbs->shared;
- struct cpufreq_policy *policy;
unsigned long flags;

spin_lock_irqsave(&shared->timer_lock, flags);
- policy = shared->policy;

/*
* Timer handler isn't allowed to queue work at the moment, because:
@@ -277,13 +275,11 @@ static void dbs_timer_handler(unsigned long data)
* - We are stopping the governor
* - Or we are updating the sampling rate of ondemand governor
*/
- if (shared->skip_work)
- goto unlock;
-
- shared->skip_work++;
- queue_work(system_wq, &shared->work);
+ if (!shared->skip_work) {
+ shared->skip_work++;
+ queue_work(system_wq, &shared->work);
+ }

-unlock:
spin_unlock_irqrestore(&shared->timer_lock, flags);
}

I will resend this patch now.

--
viresh