linux-kernel - Re: cgroup, RT reservation per core(s)?

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Date:	Tue, 10 Feb 2009 14:06:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Rolando Martins <rolando.martins@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: cgroup, RT reservation per core(s)?

On Mon, 2009-02-09 at 20:04 +0000, Rolando Martins wrote:

> I should have elaborated this more:
> 
>                      root
>                   ----|----
>                   |          |
> (0.5 mem) 0         1 (100% rt, 0.5 mem)
>                          ---------
>                          |    |    |
>                          2   3   4  (33% rt for each group, 33% mem
> per group(0.165))
> Rol

Right, i think this can be done.

You would indeed need cpusets and sched-cgroups.

Split the machine in 2 using cpusets.

   ___R___
  /       \
 A         B

Where R is the root cpuset, and A and B are the siblings.
Assign A one half the cpus, and B the other half.
Disable load-balancing on R.

Then using sched cgroups create the hierarchy

  ____1____
 /    |    \
2     3     4

Where 1 can be the root group if you like.

Assign 1 a utilization limit of 100%, and 2,3 and 4 a utilization limit
of 33% each.

Then place the tasks that get 100% cputime on your 2 cpus in cpuset A
and sched group 1.

Place your other tasks in B,{2-4} respectively.

The reason this works is that bandwidth distribution is sched domain
wide, and by disabling load-balancing on R, you split the schedule
domain.

I've never actually tried anything like this, let me know if it
works ;-)
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