[PATCH 07/41] cpuset: Set up interface for nohz flag

[Peter Zijlstra]

On Tue, 2012-05-08 at 16:20 +0200, Frederic Weisbecker wrote:
> 2012/5/7 Christoph Lameter <cl at linux.com>:
> > On Tue, 1 May 2012, Frederic Weisbecker wrote:
> >
> >> Prepare the interface to implement the nohz cpuset flag.
> >> This flag, once set, will tell the system to try to
> >> shutdown the periodic timer tick when possible.
> >>
> >> We use here a per cpu refcounter. As long as a CPU
> >> is contained into at least one cpuset that has the
> >> nohz flag set, it is part of the set of CPUs that
> >> run into adaptive nohz mode.
> >
> > As I have said before: It would be much simpler if one could specify the
> > set of nohz cpus independently of cpusets. Having a flag f.e. as a file in
> >
> >        /sys/devices/system/cpu/cpuX/nohz
> 
> I don't know if it would be simpler. It's just a different interface
> to set a per-CPU property.
> Cpusets of sysfs, I don't mind either way.
> 
> What is the usual policy on where to put which kind of CPU property?

There's no such policy, but I don't get why Christoph objects to
cpusets, its the option I would prefer. You're going to use cpusets
anyway to partition your system, might as well also use it to mark a
whole partition/set as nohz.