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SubjectRe: [PATCH 05/31] cpumask: Provide new cpumask API

* Mike Travis <travis@sgi.com> wrote:

> Mike Travis wrote:
> > Ingo Molnar wrote:
> ...
> >
> >> In what way will Rusty's changes differ? Since you incorporate some of
> >> Rusty's changes already, could you please iterate towards a single
> >> patchset which we could then start testing?
> >
> > Our timezones are not very conducive to a lot of email exchanges
> > (and he's moving.) From what I've seen I believe he's leaning
> > towards using struct cpumask * and less trickery than I have.

actually, that's quite sane to do. const_cpumask_t looked a bit weird to
me.

the extra indirection to a cpumask_t is not a big issue IMO, so in that
sense whether we pass by value or pass by reference is not a _big_
performance item.

The complications (both present and expected ones) all come from the
allocations.

> Oh yeah, I forgot the other major point of Rusty's approach. He wants
> the patchset to be completely bisectable. That's far from true in my
> version.

well, it should be a smooth transition and completely bisectable,
there's hundreds of usages of cpumask_t and quite many in the pipeline.
It's far easier to _you_ to get this stuff to work if it's all gradual
and is expected to work all across. Have a default-off debug mode that
turns off compatible cpumask_t perhaps - we can remove that later on.

with 'struct cpumask' we could keep cpumask_t as the compatible API, and
could see the impact of these changes in a very finegrained and gradual
way. Seems like a fundamentally sane approach to me ...

Ingo


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