Re: [PATCH][RFC] make cpu_sibling_map a cpumask_t

[James Cleverdon]

On Sunday 07 December 2003 8:25 pm, Nick Piggin wrote:
> Hi guys,
> This is rather a trivial change but is not for 2.6.0.
> The patch is actually on top of some of my HT stuff so one part is
> slightly different, but its purpose is to gather feedback.
>
> It turns the cpu_sibling_map array from an array of cpus to an array
> of cpumasks. This allows handling of more than 2 siblings, not that
> I know of any immediate need.

There will probably be a need, although I don't know how soon.  Some of the 
Intel folks have not been hinting that there will be more than two siblings 
in a future CPU.  No, they have not been hinting at all.   ;^)


> I think it generalises cpu_sibling_map sufficiently that it can become
> generic code. This would allow architecture specific code to build the
> sibling map, and then Ingo's or my HT implementations to build their
> scheduling descriptions in generic code.
>
> I'm not aware of any reason why the kernel should not become generally
> SMT aware. It is sufficiently different to SMP that it is worth
> specialising it, although I am only aware of P4 and POWER5 implementations.
>
> Best regards
> Nick
>
> P.S.
> I have an alternative to Ingo's HT scheduler which basically does
> the same thing. It is showing a 20% elapsed time improvement with a
> make -j3 on a 2xP4 Xeon (4 logical CPUs).
>
> Before Ingo's is merged, I would like to discuss the pros and cons of
> both approaches with those interested. If Ingo's is accepted I should
> still be able to port my other SMP/NUMA improvements on top of it.

-- 
James Cleverdon
IBM xSeries Linux Solutions
{jamesclv(Unix, preferred), cleverdj(Notes)} at us dot ibm dot comm
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