[lkml]   [2014]   [May]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [Query]: tick-sched: why don't we stop tick when we are running idle task?
On Wed, May 14, 2014 at 01:30:39AM +0200, Frederic Weisbecker wrote:
> On Fri, May 09, 2014 at 02:14:10PM +0530, Viresh Kumar wrote:
> > On 23 April 2014 16:42, Viresh Kumar <> wrote:
> > > On 15 April 2014 15:00, Frederic Weisbecker <> wrote:
> > >> Ok, I'm a bit buzy with a conference right now but I'm going to summarize that
> > >> soonish.
> >
> > Hi Frederic,
> >
> > Please see if you can find some time to close this, that would be very
> > helpful :)
> >
> > Thanks
> I'm generally worried about the accounting in update_curr() that periodically
> updates stats. I have no idea which of these stats could be read by other CPUs:
> vruntime, load bandwitdth, etc...

update_curr() principally does the sum_exec_runtime and vruntime. Now
vruntime is only interesting for other cpus when moving tasks across
CPUs, so see below on load-balancing.

sum_exec_runtime is used for a number of task stats, but when nobody
looks at those it shouldn't matter.

So rather than constantly force update them for no purpose, update them
on-demand. So when someone reads those cputime stats, prod the task/cpu.
I think you can do a remote update_curr() just fine.

And I suppose you also need to do something with task_tick_numa(), that
relies on the tick regardless of nr_running. And that's very much not
something you can do remotely. As it stands I think the numa balancing
and nohz_full are incompatible.

> Also without tick:
> * we don't poll anymore on trigger_load_balance()
> * __update_cpu_load() requires fixed rate periodic polling. Alex Shi had
> patches for that but I'm not sure if that's going to be merged
> * rq->rt_avg accounting?

So I think typically we don't want load-balancing to happen when we're
on a nohz_full cpu and there's only the one task running.

So what you can do is extend the existing nohz balancing (which
currently only deals with CPU_IDLE) to also remote balance CPU_NOT_IDLE
when nr_running == 1.

[unhandled content-type:application/pgp-signature]
 \ /
  Last update: 2014-05-22 11:21    [W:0.067 / U:0.140 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site