lkml.org 
[lkml]   [2018]   [May]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] schedutil: Allow cpufreq requests to be made even when kthread kicked
Hi Viresh,
thanks for clarifying...

On 22-May 15:53, Viresh Kumar wrote:
> On 21-05-18, 10:20, Joel Fernandes wrote:
> > On Mon, May 21, 2018 at 06:00:50PM +0100, Patrick Bellasi wrote:
> > > If that's the case, this means that if, for example, during a
> > > frequency switch you get a request to reduce the frequency (e.g.
> > > deadline task passing the 0-lag time) and right after a request to
> > > increase the frequency (e.g. the current FAIR task tick)... you will
> > > enqueue a freq drop followed by a freq increase and actually do two
> > > frequency hops?
>
> I don't think so.
>
> Consider the kthread as running currently and has just cleared the
> work_in_progress flag. Sched update comes at that time and we decide
> to reduce the frequency, we queue another work and update next_freq.
> Now if another sched update comes before the kthread finishes its
> previous loop, we will simply update next_freq and return. So when the
> next time kthread runs, it will pick the most recent update.

Mmm... right... looking better at the two execution contexts:

// A) Frequency update requests
sugov_update_commit() {
sg_policy->next_freq = next_freq;
if (!sg_policy->work_in_progress) {
sg_policy->work_in_progress = true;
irq_work_queue(&sg_policy->irq_work);
}
}

// B) Actual frequency updates
sugov_work() {
freq = sg_policy->next_freq;
sg_policy->work_in_progress = false;

__cpufreq_driver_target(sg_policy->policy, freq, CPUFREQ_RELATION_L);
}


It's true that A will enqueue only one B at the first next_freq update
and then it will keep just updating the next_freq.
Thus, we should be ensure to have always just one kwork pending in the
queue.

> Where is the problem both of you see ?

Perhaps the confusion comes just from the naming of
"work_in_progress", which is confusing since we use it now to
represent that we enqueued a frequency change and we wait for the
kwork to pick it up.

Maybe it can help to rename it to something like kwork_queued or
update_pending, update_queued... ?


--
#include <best/regards.h>

Patrick Bellasi

\
 
 \ /
  Last update: 2018-05-22 12:39    [W:0.075 / U:1.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site