[PATCH 0/5] Kernel mode NEON for XOR and RAID6

Dave Martin dave.martin at linaro.org
Tue Jun 25 10:29:13 EDT 2013

On Tue, Jun 25, 2013 at 04:14:13PM +0200, Ard Biesheuvel wrote:
> On 25 June 2013 15:56, Dave Martin <dave.martin at linaro.org> wrote:
> > Significant benchmarks on the boot path would be unacceptable, unless they
> > are *fast* (and by fast, I mean fast on all platforms, not just fast on
> > the fast platforms).  If one second gets added onto the boot path for each
> > optimised algorithm, that sounds like a fail.  If all the benchmarks
> > combined take one second in total, that's no quite as bad.
> >
> > Maybe benchmarks could be time-bounded (i.e., see how much data we can
> > chug though in X milliseconds) instead of size-bounded.  This would avoid
> > unreasonable slowdown on slow platforms, while avoiding trivially small
> > benchmark payloads on faster platforms which may typically have a more
> > complex architecture, bigger caches etc. which would cause them to take
> > longer to reach saturated performance when running a particular algorithm.
> >
> Benchmarks are already time bounded, at least the instances I am aware
> of (xor and raid6) are. They each measure, for each available
> implementation, the amount of work performed during a fixed time. For
> RAID6, this is 16 jiffies, for XOR it's only 1 jiffy but each test is
> repeated 5 times.
> So I think this should not be a problem, especially as it is unlikely
> that newly added implementations (such as NEON) will be able to
> execute on older/slower platforms in the first place.

The tree I was originally looking at might be out of date ... apologies
for the trolling.

If the XOR benchmark really only takes 50 ms per implementation, I guess
that shouldn't be too bad.


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