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SubjectRe: [PATCH] Athlon/Opteron Prefetch Fix for 2.6.0test5 + numbers
Andi Kleen <ak@suse.de> wrote:
>
>
> This is much more efficient than the previous workaround used in the kernel,
> which checked for AMD CPUs in every prefetch(). This can be seen
> in the size of the vmlinux:

That is hardly a serious comparison: the workaround is just to stop the
oopses while this gets sorted out. It makes no pretense at either
efficiency or permanence.

> Without patch:
> text data bss dec hex filename
> 4020232 665956 169092 4855280 4a15f0 vmlinux
> With patch:
> 4011578 665973 169092 4846643 49f433

hrm. Why did data grow?

> With prefetch check: 3.7268 microseconds
> Without prefetch check: 3.65945 microseconds

We don't know how much of this difference is due to removing the branch and
how much is due to reenabling prefetch.

It would be interesting to see comparative benchmarking between prefetch
and no prefetch at all, see whether this feature is worth its icache
footprint.

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