On 09-05-18, 02:02, Joel Fernandes wrote:
> On Wed, May 09, 2018 at 02:10:01PM +0530, Viresh Kumar wrote:
> > Right, none of the above changes are required now.
>
> I didn't follow what you mean the changes are not required? I was developing
> against Linus mainline. Also I replied to Rafael's comment in the other
> thread.
At least for the shared policy case the entire sequence of
sugov_should_update_freq() followed by sugov_update_commit() is
executed from within spinlock protected region and you are using the
same lock below. And so either the above two routines or the kthread
routine below will execute at a given point of time.
So in case kthread has started doing the update and acquired the lock,
the util update handler will wait until the time work_in_progress is
set to false, that's not a problem we are trying to solve here.
And if kthread hasn't acquired the lock yet and util handler has
started executing sugov_should_update_freq() ....
And ^^^ this is where I understood that your earlier change is
actually required, so that we accumulate the latest updated next_freq
value.
And with all that we wouldn't require a while loop in the kthread
code.
> > > > @@ -381,13 +381,23 @@ sugov_update_shared(struct update_util_data
> > > > *hook, u64 time, unsigned int flags)
> > > > static void sugov_work(struct kthread_work *work)
> > > > {
> > > > struct sugov_policy *sg_policy = container_of(work, struct
> > > > sugov_policy, work);
> > > > + unsigned int freq;
> > > > +
> > > > + /*
> > > > + * Hold sg_policy->update_lock just enough to handle the case
> > > > where:
> > > > + * if sg_policy->next_freq is updated before work_in_progress
> > > > is set to
> > > > + * false, we may miss queueing the new update request since
> > > > + * work_in_progress would appear to be true.
> > > > + */
> > > > + raw_spin_lock(&sg_policy->update_lock);
> > > > + freq = sg_policy->next_freq;
> > > > + sg_policy->work_in_progress = false;
> > > > + raw_spin_unlock(&sg_policy->update_lock);
> >
> > One problem we still have is that sg_policy->update_lock is only used
> > in the shared policy case and not in the single CPU per policy case,
> > so the race isn't solved there yet.
>
> True.. I can make the single CPU case acquire the update_lock very briefly
> around sugov_update_commit call in sugov_update_single.
Rafael was very clear from the beginning that he wouldn't allow a spin
lock in the un-shared policy case :)
--
viresh
