Re: [PATCH] x86: eliminate redundant/contradicting cache line size config options

Arjan van de Ven
2009-11-19T04:51:00Z

On Thu, 19 Nov 2009 04:56:40 +0100
Ingo Molnar <mingo@elte.hu> wrote:

>
> * Nick Piggin <npiggin@suse.de> wrote:
>
> > The only other use for L1 cache size macro is to pack objects to
> > cachelines better (so they always use the fewest number of lines).
> > But this case is more rare nowadays people don't really count
> > cachelines anymore, but I think even then it makes sense for it to
> > be the largest line size in the system because we don't know how
> > big L1s are, and if you want opimal L1 packing, you likely also
> > want optimal Ln packing.
>
> We could do that - but then this default of X86_INTERNODE_CACHE_SHIFT:
>
> + default "7" if NUMA
>
> will bite us and turns the 64 bytes L1_CACHE_BYTES into an effective
> 128 bytes value.
>
> So ... are you arguing for an increase of the default x86 linesize to
> 128 bytes?

128 is basically always wrong.
(unless you have a P4... but for default really we should not care
about those anymore)

--
Arjan van de Ven Intel Open Source Technology Centre
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