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

[Ard Biesheuvel]

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.

Regards,
Ard.