Ingo Molnar wrote:
* Nick Piggin <[email protected]> wrote:
This is Suresh's patch with some modifications.
Remove degenerate scheduler domains during the sched-domain init.
actually, i'd suggest to not do this patch. The point of booting with a
CONFIG_NUMA kernel on a non-NUMA box is mostly for testing, and the
'degenerate' toplevel domain exposed conceptual bugs in the
sched-domains code. In that sense removing such 'unnecessary' domains
inhibits debuggability to a certain degree. If we had this patch earlier
we'd not have experienced the wrong decisions taken by the scheduler,
only on the much rarer 'really NUMA' boxes.
True. Although I'd imagine it may be something distros may want.
For example, a generic x86-64 kernel for both AMD and Intel systems
could easily have SMT and NUMA turned on.
I agree with the downside of exercising less code paths though.
What about putting as a (default to off for 2.6) config option in
the config embedded menu?
is there any case where we'd want to simplify the domain tree? One more
domain level is just one (and very minor) aspect of CONFIG_NUMA - i'd
not want to run a CONFIG_NUMA kernel on a non-NUMA box, even if the
domain tree got optimized. Hm?
I guess there is the SMT issue too, and even booting an SMP kernel
on a UP system. Also small ia64 NUMA systems will probably have one
redundant NUMA level.
If/when topologies get more complex (for example, the recent Altix
discussions we had with Paul), it will be generally easier to set
up all levels in a generic way, then weed them out using something
like this, rather than put the logic in the domain setup code.
Nick
--
SUSE Labs, Novell Inc.
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