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

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Date:	Wed, 11 Feb 2009 12:10:06 +0000
From:	Rolando Martins <rolando.martins@...il.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Paul Menage <menage@...gle.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: cgroup, RT reservation per core(s)?

On 2/11/09, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> * Peter Zijlstra <peterz@...radead.org> [2009-02-11 12:42:14]:
>
>
>  > On Wed, 2009-02-11 at 11:33 +0000, Rolando Martins wrote:
>  >
>  > > Hi again,
>  > >
>  > > is there any way to have multiple "distinct" sched domains, i.e.:
>  > > mount -t cgroup -o cpu none /dev/sched_domain_0
>  > > .... setup sched_domain_0 (ex:  90% RT, 10% Others)
>  > > mount -t cgroup -o cpu none /dev/sched_domain_1
>  > > .... setup sched_domain_1 (ex:  20% RT, 80% Others)
>  > > Then give sched_domain_0 to cpuset A and sched_domain_1 to B?
>  >
>  > Nope.
>  >
>  > We currently only support a single instance of a cgroup controller.
>  >
>  > I see the use for what you propose, however implementing that will be
>  > 'interesting'.
>
>
> I am confused, if you cpusets, you get your own sched_domain. If you
>  mount cpusets and cpu controller together, you'll get what you want.
>  Is this a figment of my imagination. You might need to use exclusive
>  CPUsets though.
>
>  --
>
>         Balbir
>
I don't know if you meant the following situation (mounting cpuset and
cpu together):

                                                            R
                                              -----------------------
      (80% RT, 20%Others)      A                        B (100% RT, 0%
Others)
      (Cpus 0-2)                                                 (CPU 3)

If so, we can't do this because  of the restriction imposed by global
rt_runtime_ns.
Perhaps a "feasible" solution could be implemented by having distinct
global rt_runtime_ns (one for each cpu, i.e.: rt_runtime_ns_0; ...;
rt_runtime_n )

                                                            R
                                              -----------------------
      (80% RT, 20%Others)      A                        B (100% RT, 0%
Others)
      (Cpus 0-2)                                                 (CPU 3)
capacity_used_cpu_0_rt = 0.8                        capacity_used_cpu_3_rt = 1
capacity_used_cpu_1_rt = 0.8
capacity_used_cpu_2_rt = 0.8

Given a i processor: we have the global restriction enforced:
SUM(capacity_used_cpu_i_rt) < rt_runtime_i

Rol
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