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SubjectRe: [PATCH] x86: Run checksumming in parallel accross multiple alu's

* 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

This patch should really come with measurement numbers: what performance
increase (and drop) did you get on what CPUs.


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