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SubjectRe: [PATCH v2 2/2] x86: add prefetching to do_csum
On Wed, Nov 06, 2013 at 10:23:19AM -0500, Neil Horman wrote:
> do_csum was identified via perf recently as a hot spot when doing
> receive on ip over infiniband workloads. After alot of testing and
> ideas, we found the best optimization available to us currently is to
> prefetch the entire data buffer prior to doing the checksum
>
> diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
> index 9845371..9f2d3ee 100644
> --- a/arch/x86/lib/csum-partial_64.c
> +++ b/arch/x86/lib/csum-partial_64.c
> @@ -29,8 +29,15 @@ static inline unsigned short from32to16(unsigned a)
> * Things tried and found to not make it faster:
> * Manual Prefetching
> * Unrolling to an 128 bytes inner loop.
> - * Using interleaving with more registers to break the carry chains.

Did you mean perhaps to remove the "Manual Prefetching" line instead ?
(Curious, what was tried before that made it not worthwhile?)

Dave



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