* Ingo Molnar <[email protected]> wrote:
> This introduces a ~1msec delay and thus simulates IO, but the
> delays are *constant* [make sure you use a high-res timers kernel],
> so they do not result in nearly as much measurement noise as real
> block IO does.
>
> The IO delays will still be there, so any caching advantages (and
> CPU overhead reductions) will be measurable very clearly.
>
> This way you are basically 'emulating' a real disk drive but you
> will emulate uniform latencies, which makes measurements a lot more
> reliable - while still relevant to the end result.
>
> So if under such a measurement model you can prove an improvement
> with a patch, that improvement will be there with real disks as
> well - just harder to prove.
Another risk that the current situation carries in itself, beyond
making it more difficult to measure improvements, is that based on a
"bad" Bonnie outlier or artifact you might throw away a perfectly
good change accidentally!
So whenever you think you are fighting noise you need to improve your
measurements, as entropy is a pretty tough opponent to beat.
Thanks,
Ingo
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