[PATCH 0/5] IP checksum improvements

Joakim Tjernlund joakim.tjernlund at transmode.se
Sun Apr 25 23:54:46 CEST 2010

Ondrej Zajicek <santiago at crfreenet.org> wrote on 2010/04/25 23:20:52:
> On Sun, Apr 25, 2010 at 11:41:17AM +0200, Joakim Tjernlund wrote:
> > Here are a series of performance improvements on the
> > Internet checksum. With these changes applied I get about
> > 20-30% better performance on x86 and PowerPC.
> Although i agree with Martin Mares that such kind of optimizations
> should be done mainly if we know (from profiling) that BIRD spends
> a significant share of time (during update processing) in that function,
> i did some changes to the checksum function and merged some of these
> patches.
> I did some more optimizations (changing the loop condition, removing len
> decrement) and together with your change to add32 i got two times faster
> checksum function (on x86) than the old code. Changing postincrement to
> preincrement leads to worse results (only 1.4 times faster than the old
> code) so i kept postincrement.

On x86? That is strange. On x86 that should only lead to one
extra add outside the loop, or so I think.

the while(buf < end) definitely slower on any RISC like CPU. Did you test
for (; len; --len)
     sum = addr32(sum, *buf++);
Was  the other arch's also faster with that?


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