Re: [PATCH 00/10] vtime: Delay cputime accounting to tick

[Martin Schwidefsky]

On Tue, 6 Dec 2016 15:20:55 +1100
Paul Mackerras <paulus@xxxxxxxxxx> wrote:

> On Tue, Dec 06, 2016 at 03:32:13AM +0100, Frederic Weisbecker wrote:
> > This follows up Martin Schwidefsky's patch which propose to delay
> > cputime accounting to the tick in order to minimize the calls to
> > account_system_time() and alikes as these functions can carry quite some
> > overhead:
> > 
> > 	http://lkml.kernel.org/r/20161121111728.13a0a3db@mschwide
> > 
> > The set includes Martin's patch, rebased on top of tip:sched/core and
> > latest s390 changes, and extends it to the other implementations of
> > CONFIG_VIRT_CPU_ACCOUNTING_NATIVE (powerpc and ia64) along with a few
> > core changes to adapt the whole.
> > 
> > Only built-tested though as I don't have access to any of these archs.  
> 
> The patches look reasonable at a quick look.  I assume that to test
> them, we would want to run a guest in an overcommitted system, so as
> to get some steal time.  Do you have any more specific suggestions as
> to what to run as a test?  Just run some benchmark and see if the
> user/system/irq times look reasonable?  Or do you have something more
> quantitative?

My quick test this morning showed that for s390 it works quite well. 
I yet have to do more detailed tests to see if the numbers really
add up.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.