Some cache related optimizations

[shurd]

Summary

1. prefetch 128 bytes of mbufs.
2. Re-order filling the pkt_info so cache stalls happen at the end
3. Define empty prefetch2() macro when the function isn't present.

Provides small performance improvments on some hardware

Test Plan

Test on a wider range of hardware for regressions

[sbruno]

Is there a reason that we don't modify prefetch() instead of creating a new prefetch2() function?

[shurd]

In D12447#258276, @sbruno wrote:

Is there a reason that we don't modify prefetch() instead of creating a new prefetch2() function?

The majority of places prefetch() is used don't need the extra cacheline prefetched.

[sbruno]

Ok, lets rename prefetch2() to something that indicates why there is a second function (being a bit pedantic here). something like prefetch_align() or whatever.

[shurd]

In D12447#259600, @sbruno wrote:

Ok, lets rename prefetch2() to something that indicates why there is a second function (being a bit pedantic here). something like prefetch_align() or whatever.

Do you like prefetch2cachelines() better?

[sbruno]

In D12447#261301, @shurd wrote:

In D12447#259600, @sbruno wrote:

Ok, lets rename prefetch2() to something that indicates why there is a second function (being a bit pedantic here). something like prefetch_align() or whatever.

Do you like prefetch2cachelines() better?

I think that's fine. It at least explains what's up with this function.

[shurd]

Rename prefecth2() to prefetch2cachelines()