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

Paul Mackerras
2016-12-06T04:21:02Z

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?

Paul.