Re: [Lse-tech] [RFC PATCH] scheduler: Dynamic sched_domains

[Matthew Dobson <colpatch@us.ibm.com>]

On Fri, 2004-10-08 at 03:40, Nick Piggin wrote:
> And so you want to make a partition with CPUs {0,1,2,4,5}, and {3,6,7}
> for some crazy reason, the new domains would look like this:
> 
> 0 1  2  4 5    3  6 7
> ---  -  ---    -  ---  <- 0
>   |   |   |     |   |
>   -----   -     -   -   <- 1
>     |     |     |   |
>     -------     -----   <- 2 (global, partitioned)
> 
> Agreed? You don't need to get fancier than that, do you?
> 
> Then how to input the partitions... you could have a sysfs entry that
> takes the complete partition info in the form:
> 
> 0,1,2,3 4,5,6 7,8 ...
> 
> Pretty dumb and simple.

How do we describe the levels other than the first?  We'd either need
to:
1) come up with a language to describe the full tree.  For your example
I quoted above:
   echo "0,1,2,4,5 3,6 7,8;0,1,2 4,5 3 6,7;0,1 2 4,5 3 6,7" > partitions

2) have multiple files:
   echo "0,1,2,4,5 3,6,7" > level2
   echo "0,1,2 4,5 3 6,7" > level1
   echo "0,1 2 4,5 3 6,7" > level0

3) Or do it hierarchically as Paul implemented in cpusets, and as I
described in an earlier mail:
   mkdir level2
   echo "0,1,2,4,5 3,6,7" > level2/partitions
   mkdir level1
   echo "0,1,2 4,5 3 6,7" > level1/partitions
   mkdir level0
   echo "0,1 2 4,5 3 6,7" > level0/partitions

I personally like the hierarchical idea.  Machine topologies tend to
look tree-like, and every useful sched_domain layout I've ever seen has
been tree-like.  I think our interface should match that.

-Matt