* Prasad Joshi <prasadjoshi124@xxxxxxxxx> wrote: > Summary of performance numbers > ============================== > There is not much difference with sequential character operations are > performed, the code with caching performed better by small margin. The caching > code performance raised by 12% with sequential block output and dropped by > 0.5% with sequential block input. The caching code also suffered with > Random seeks and performed badly by 12%. The performance numbers drastically > improved with sequential creates (62%) and delete operations (30%). Looking at the numbers i think it's pretty clear that from this point on the quality of IO tests should be improved: Bonnie is too noisy and does not cut it anymore for finer enhancements. To make measurements easier you could also do a simple trick: put *all* of the disk image into /dev/shm and add a command-line debug option that add a fixed-amount udelay(1000) call every time the code reads from the disk image. 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. Wanna try this? I really think you are hitting the limits of your current measurement methodology and you will be wasting time running more measurements instead of saving time doing more intelligent measurements ;-) 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
