Messages in this thread | | | Date | Tue, 1 Apr 2008 17:42:38 +0530 | From | Srivatsa Vaddagiri <> | Subject | Re: [RFC/PATCH 01/17] sched: mix tasks and groups |
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On Sun, Mar 09, 2008 at 06:08:51PM +0100, Peter Zijlstra wrote: > This patch allows tasks and groups to exist in the same cfs_rq. With this > change the CFS group scheduling follows a 1/(M+N) model from a 1/(1+N) > fairness model where M tasks and N groups exist at the cfs_rq level. > > [a.p.zijlstra@chello.nl: rt bits] > Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com> > Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > --- > kernel/sched.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++-- > kernel/sched_fair.c | 48 +++++++++++++++++++++++++++++++++++++++++++--- > kernel/sched_rt.c | 15 ++++++++------ > 3 files changed, 106 insertions(+), 11 deletions(-) > > Index: linux-2.6-2/kernel/sched.c > =================================================================== > --- linux-2.6-2.orig/kernel/sched.c > +++ linux-2.6-2/kernel/sched.c > @@ -273,18 +273,23 @@ struct task_group { > }; > > #ifdef CONFIG_FAIR_GROUP_SCHED > + > +#ifdef CONFIG_USER_SCHED > /* Default task group's sched entity on each cpu */ > static DEFINE_PER_CPU(struct sched_entity, init_sched_entity); > /* Default task group's cfs_rq on each cpu */ > static DEFINE_PER_CPU(struct cfs_rq, init_cfs_rq) ____cacheline_aligned_in_smp; > +#endif
I am trying to understand the change this brings for semantics of RT-scheduling.
With this change, /cgroup will be seen as the parent group of all other groups (say: /cgroup/A, /cgroup/B etc). Is that correct?
If so, the check in __rt_schedulable() needs a change as well, which assumes that all task groups form a flat hierarchy.
For example: lets say that init_task_group (/cgroup in this case) had the default rt_bandwidth of 95% (global_rt_runtime()). A child group under it (/cgroup/A) is created. If user tries to assign it a rt-bandwidth of 50%, then AFAICS, it will fail with current code, whereas it shouldn't (because by giving /cgroup/A 50% bandwidth, we are not really exceeding the globally allowed RT bandwidth of 95%, since /cgroup/A is a child of /cgroup).
-- Regards, vatsa
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