[Devel] Re: [PATCH 1/1, v6] cgroup/freezer: add per freezer duty ratio control

[Matt Helsley]

On Thu, Feb 10, 2011 at 02:22:21PM -0800, jacob pan wrote:
> On Thu, 10 Feb 2011 11:11:17 -0800
> Matt Helsley <matthltc at us.ibm.com> wrote:
> 
> > On Wed, Feb 09, 2011 at 07:06:15PM -0800, Arjan van de Ven wrote:
> > > On 2/9/2011 7:04 PM, Matt Helsley wrote:
> > > >On Tue, Feb 08, 2011 at 05:05:41PM -0800,
> > > >jacob.jun.pan at linux.intel.com wrote:
> > > >>From: Jacob Pan<jacob.jun.pan at linux.intel.com>
> > > >>
> > > >>Freezer subsystem is used to manage batch jobs which can start
> > > >>stop at the same time. However, sometime it is desirable to let
> > > >>the kernel manage the freezer state automatically with a given
> > > >>duty ratio.
> > > >>For example, if we want to reduce the time that backgroup apps
> > > >>are allowed to run we can put them into a freezer subsystem and
> > > >>set the kernel to turn them THAWED/FROZEN at given duty ratio.
> > > >>
> > > >>This patch introduces two file nodes under cgroup
> > > >>freezer.duty_ratio_pct and freezer.period_sec
> > > >>
> > > >>Usage example: set period to be 5 seconds and frozen duty ratio
> > > >>90% [root at localhost aoa]# echo 90>  freezer.duty_ratio_pct
> > > >>[root at localhost aoa]# echo 5000>  freezer.period_ms
> > > >I kept wondering how this was useful when we've got the "cpu"
> > > >subsystem because for some reason "duty cycle" made me think this
> > > >was a scheduling policy knob. In fact, I'm pretty sure it is -- it
> > > >just happens to sometimes reduce power consumption.
> > > >
> > > >Have you tried using the cpu cgroup subsystem's share to see if it
> > > >can have a similar effect?
> > > 
> > > does the cpu cgroup system work on a 20 to 30 second time window?
> > 
> > I don't think so -- it works directly with the scheduler IIRC.
> > 
> I played with cpu subsystem a little today, it is for real-time tasks
> only. By data type of cpu.rt_period_us  cpu.rt_runtime_us, it
> actually has a pretty long time window (35 mins, int type at usec
> resolution).
> For some reason, I could not even get cpu subsystem to work with RT
> task to work on 38-rc2 kernel. Here is what I did
> - mount and create cpu cgroup fs
> - launch task with SCHED_RR
> - attach task to my newly created cgroup
> - adjust cpu.rt_period_us  cpu.rt_runtime_us
> But it never changed percentage of runtime. The ask in the cpu cgroup
> always run at 100% or more than the runtime_us as I specified. I have
> tried both with system idle and background tasks.
> 
> I do agree that dealing with group scheduler directly might be more
> natural. but the hurdle might be changing cpu subsystem to support
> non-rt, and deal with scheduler heuristics.

Even though it probably requires more effort that seems like the right
approach.

Cheers,
	-Matt Helsley
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