On 10/11/2013 09:51 AM, Neil Horman 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
On hardware that implement ADCX/ADOX then you should also be able to
have additional streams interleaved since those instructions allow for
dual carry chains.
-hpa
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