On Sat, Oct 12, 2013 at 07:21:24PM +0200, Ingo Molnar wrote: > > * Neil Horman <nhor...@tuxdriver.com> wrote: > > > Sébastien Dugué reported to me that devices implementing ipoib (which > > don't have checksum offload hardware were spending a significant amount > > of time computing checksums. We found that by splitting the checksum > > computation into two separate streams, each skipping successive elements > > of the buffer being summed, we could parallelize the checksum operation > > accros multiple alus. Since neither chain is dependent on the result of > > the other, we get a speedup in execution (on hardware that has multiple > > alu's available, which is almost ubiquitous on x86), and only a > > negligible decrease on hardware that has only a single alu (an extra > > addition is introduced). Since addition in commutative, the result is > > the same, only faster > > This patch should really come with measurement numbers: what performance > increase (and drop) did you get on what CPUs. > > Thanks, > > Ingo >
So, early testing results today. I wrote a test module that, allocated a 4k buffer, initalized it with random data, and called csum_partial on it 100000 times, recording the time at the start and end of that loop. Results on a 2.4 GHz Intel Xeon processor: Without patch: Average execute time for csum_partial was 808 ns With patch: Average execute time for csum_partial was 438 ns I'm looking into hpa's suggestion to use alternate instructions where available right now. I'll have more soon Neil -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
