* Ingo Molnar <mingo@xxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
