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

[Nick Piggin <nickpiggin@yahoo.com.au>]

Takayoshi Kochi wrote:

> Yup, if SD_NODES_PER_DOMAIN is set to 4, our 32-way TX-7 have 
> two disjoint domains ;(
> (though the current default is 6 for ia64...)
> 
> I think the default configuration of the scheduler domains should be
> as identical to its real hardware topology as possible, and should
> modify the default only when necessary (e.g. for Altix).
> 

That is the idea. Unfortunately the ia64 modifications are ia64 wide.
I don't think it should be too hard to make it sn2 only.

> Right now with the sched domain scheduler, we have to setup the 
> domain hierarcy only at boot time statically, which makes it harder to
> find the optimal domain topology/parameter.  The dynamic patch
> makes it easier to modify the default configuration.
> 

No you don't have to. If you have a look at the work in -mm, basically
the whole thing gets recreated on every hoplug operation. It would be
trivial to modify some parameters then reinit the domains in the same
way.

N disjoint domains can be trivially handled by making N passes over
the init code, each using a different set of CPUs as its
"cpu_possible_map". This can easily be done dynamically by using
the above method.

> If the scheduler gains more dynamic configurability like what Jesse
> said, it adds more flexibility for runtime optimization and seems
> a way to go.  I'm not sure runtime configurability of domain topology
> is necessary for all users, but it's extremely useful for developers.
> 

That would be nice. The patch queue is pretty well clogged up at the
moment, so I'm not going to look at the scheduler again until all the
patches from -mm get into 2.6.10-bk.