Re: [PATCH v2 2/2] x86: add prefetching to do_csum

From: Andi Kleen
Date: Wed Nov 06 2013 - 15:20:00 EST

Neil Horman <nhorman@xxxxxxxxxxxxx> writes:

> 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

On what CPU? Most modern CPUs should not have any trouble at all
prefetching a linear access.

Also for large buffers it is unlikely that all the prefetches
are actually executed, there is usually some limit.

As a minimum you would need:
- run it with a range of buffer sizes
- run this on a range of different CPUs and show no major regressions
- describe all of this actually in the description

But I find at least this patch very dubious.


ak@xxxxxxxxxxxxxxx -- Speaking for myself only
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