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

[Nick Piggin]

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.
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