Re: boot cgroup questions

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Mon, 2008-04-14 at 13:39 -0500, Paul Jackson wrote:
> Max wrote:
> > I mean you guys were talking about how wonderful 
> > and flexible cpusets are, but we cannot seem to use the flexibility because 
> > the apps are designed for a flat layout
> 
> No.  Not flat.  Not at all flat.
> 
> We routinely and normally have an interesting hierarchy of cpusets
> below /dev/cpuset.  However that hierarchy is determined by the
> nesting of subsets of the nodes (CPUs and/or Memory) on the system.
> 
> These subsets of nodes in the /dev/cpuset hierarchy may well map
> nicely into the subsets of CPUs that can receive a particular set
> of IRQs, however that map is not bijective.  Of particular interest
> here, it's not injective, meaning that multiple cpusets might and
> will commonly receive the same set of IRQs.  You can force this map
> to be injective by elaborating the cpuset hierarchy to reflect both
> this new assignment of IRQs and the (CPU and/or Memory) node subset
> hiearchy that it currently reflects, but that will break code that
> was expecting the directory tree below /dev/cpuset to directly and
> only reflect the node hierarchy.
> 
> In less mathematically obtuse wording, sure you can add more directory
> layers below /dev/cpuset, to handle IRQ assignments, but that will
> break code that was expecting the /dev/cpuset directory tree to only
> reflect the nesting of (CPU and/or Memory) nodes.

Sorry for being rather late to the game - other stuff keeps me from
doing anything much here :-(.

Anyway, the current applications don't support IRQ assingment anyway.
That's a new feature; and its quite common that new features require
code changes.

So I'm not seeing the problem - don't change code and stuff works as
before - change code and you get new stuff.

So I'm arguing in favour of the IRQs as tasks idea that might need extra
hierarchy levels.