On 10/07/17 22:12, Joel Fernandes wrote:
> Hi Juri,
>
> On Mon, Jul 10, 2017 at 3:55 AM, Juri Lelli <juri.le...@arm.com> wrote:
> > Hi Joel,
> >
> > On 09/07/17 10:08, Joel Fernandes wrote:
[...]
> >> static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, unsigned long
> >> *util,
> >> - unsigned long *max)
> >> + unsigned long *max, unsigned int flags)
> >> {
> >> unsigned long boost_util = sg_cpu->iowait_boost;
> >> unsigned long boost_max = sg_cpu->iowait_boost_max;
> >> @@ -195,7 +222,16 @@ static void sugov_iowait_boost(struct sugov_cpu
> >> *sg_cpu, unsigned long *util,
> >> *util = boost_util;
> >> *max = boost_max;
> >> }
> >> - sg_cpu->iowait_boost >>= 1;
> >> +
> >> + /*
> >> + * Incase iowait boost just happened on this CPU, don't reduce it
> >> right
> >> + * away since then the iowait boost will never increase on subsequent
> >> + * in_iowait wakeups.
> >> + */
> >> + if (flags & SCHED_CPUFREQ_IOWAIT && this_cpu_ptr(&sugov_cpu) ==
> >> sg_cpu)
> >> + return;
> >> +
> >> + sugov_decay_iowait_boost(sg_cpu);
> >
> > Mmm, do we need to decay even when we are computing frequency requests
> > for a domain?
> >
> > Considering it a per-cpu thing, isn't enough that it gets bumped up or
> > decayed only when a CPU does an update (by using the above from
> > sugov_update_shared)?
> >
> > If we go this way I think we will only need to reset prev_iowait_boost
> > if delta_ns > TICK_NSEC during the for_each_cpu() loop of sugov_next_
> > freq_shared().
> >
>
> Actually the "decay" was already being done before (without this
> patch), I am just preserving the same old behavior where we do decay.
> Perhaps your proposal can be a separate match? Or did I miss something
> else subtle here?
>
True, we are currently decaying anyway.
Looking again at this path made me however think if we really need to. I
guess we need currently, as we bump frenquency to max and then decay it.
But, with your changes, I was wondering if we can simplify the thing and
decay only on the per-CPU update path.
The other reason for trying to simplify this is that I don't
particularly like adding and consuming flags argument at this point, but
I guess we could refactor the code if this is really a problem.
Thanks,
- Juri
