[PATCH] Don't use SSE4_2 instructions on Intel Silvermont Micro Architecture.

[Andi Kleen]

> To see if this is a case I added Andi. Andi, could you browse sources
> and tell if you think that benchtests are adequate to measure
> performance?

It's hard to say in general and just from review.

Normally I would recommend to not run the tests in a tight loop,
but have some cache / branch prediction thrashing code in between
to measure "cache cold" behaviour too.

One objective approach to determine how good they are would be
to assemble benchmark tests on a set of non micro applications that are known
to be sensitive to memcpy/etc. performance (e.g. according to 
perf sampling). Then do a set of results for them plus run the benchmarks.

Change the memcpy et.al.  to make it slower (for example or faster if you have
a good way). Rerun the applications. Rerun the benchmarks.

Then see how the two sets of benchmark results correlate.

This would be significant work of course.

-Andi