Re: [ANNOUNCE] 3.8-rc6-nohz4

From: Steven Rostedt
Date: Fri Feb 08 2013 - 11:18:18 EST

On Fri, 2013-02-08 at 16:53 +0100, Frederic Weisbecker wrote:
> 2013/2/7 Christoph Lameter <cl@xxxxxxxxx>:
> > On Thu, 7 Feb 2013, Frederic Weisbecker wrote:
> >
> >> Not with hrtick.
> >
> > hrtick? Did we not already try that a couple of years back and it turned
> > out that the overhead of constantly reprogramming a timer via the PCI bus
> > was causing too much of a performance regression?
> Yeah Peter said that especially reprogramming the clock everytime we
> call schedule() was killing the performances. Now may be on some
> workloads, with the tick stopped, we can find some new results.

I could imagine this being dynamic. If the system isn't very loaded, and
the scheduler is giving lots of time slices to tasks, then perhaps it
could switch to a reprogramming the clock based scheduling. Or maybe, we
could switch to a "skip ticks" method. That is, instead of completely
disabling the tick, make the tick go off every other time or less, and
use the NO_HZ code to calculate the missed ticks.

-- Steve

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