Re: [PATCH v4 1/5] nohz_full: add support for "cpu_isolated" mode

Paul E. McKenney
2015-07-22T19:28:34Z

On Wed, Jul 22, 2015 at 08:57:45AM -0500, Christoph Lameter wrote:
> On Tue, 21 Jul 2015, Paul E. McKenney wrote:
>
> > > > In the current version, there's also the vmstat_update() that
> > > > may schedule delayed work and interrupt the core again
> > > > shortly before realizing that there are no more counter updates
> > > > happening, at which point it quiesces. Currently we handle
> > > > this in cpu_isolated mode simply by spinning and waiting for
> > > > the timer interrupts to complete.
> > >
> > > Perhaps we should fix that?
> >
> > Didn't Christoph Lameter fix this? Or is this an additional problem?
>
> Well the vmstat update must realize first that there are no outstanding
> updates before switching itself off. So typically there is one extra tick.
> But we could add another function that will simply fold the differential
> immediately and turn the kworker task in the expectation that the
> processor will stay quiet.

Got it, thank you!

Thanx, Paul