Re: [PATCH, v3 2/2] cgroups: introduce timer slack subsystem

["Kirill A. Shutemov" <kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>]

On Thu, Feb 03, 2011 at 11:57:43AM -0800, Jacob Pan wrote:
> On Thu, 3 Feb 2011 10:12:51 -0800
> Paul Menage <menage-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> wrote:
> 
> > On Thu, Feb 3, 2011 at 9:51 AM, Jacob Pan
> > <jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> wrote:
> > >
> > > I think this logic defeats the purpose of having timer_slack
> > > subsystem in the first place. IMHO, the original intention was to
> > > have grouping effect of tasks in the cgroup.
> > 
> > You can get the semantics you want by just setting min_slack_ns =
> > max_slack_ns.
> > 
> true. it will just make set fail when min = max. it is awkward and
> counter intuitive when you want to change the group timer_slack. you
> will have to move both min and max to clamp the value, where set
> function can not be used.

Interface is very similar to /sys/devices/system/cpu/cpuX/cpufreq.
I think it's sane. If you want some extention, you can do it with
userspace helper.

> In addition, when a parent changes min = max, I don't see the current
> code enforce new settings on the children. Am i missing something?

I've missed it. I'll fix.

> In my use case, i want to put some apps into a managed group where
> relaxed slack value is used, but when time comes to move the app out of
> that cgroup, we would like to resore the original timer slack. I see
> having a current value per cgroup can be useful if we let timer code
> pick whether to use task slack value or the cgroup slack value.
> Or we have to cache the old value per task

What's mean "original timer slack" if you are free to move a task
between a lot of cgroups and process itself free to change it anytime?

-- 
 Kirill A. Shutemov