On Tuesday 08 August 2006 07:09, Paul Mackerras wrote:
> Andrew Morton writes:
[adding linux-arch; talking about doing extensible per cpu areas
by prereserving virtual space and then later fill it up as needed]
> > > Drawback would be some more TLB misses.
> >
> > yup. On some (important) architectures - I'm not sure which architectures
> > do the bigpage-for-kernel trick.
>
> I looked at optimizing the per-cpu data accessors on PowerPC and only
> ever saw fractions of a percent change in overall performance, which
> says to me that we don't actually use per-cpu data all that much. So
> unless you make per-cpu data really really slow, I doubt that we'll
> see any significant performance difference.
The main problem is that we would need a "vmalloc reserve first; allocate pages
later" interface. On x86 it would be easy by just splitting up vmalloc/vmap a bit
again. Does anybody else see problems with implementing that on any
other architecture?
This wouldn't be truly demand paged, just pages initialized on allocation.
-Andi
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