Messages in this thread | | | Date | Thu, 4 Sep 2008 18:36:44 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC patch 0/4] TSC calibration improvements |
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* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Thu, 4 Sep 2008, Ingo Molnar wrote: > > > > ah - perhaps a dynamic statistical approach with an estimation of > > worst-case calibration error (~= standard deviation) and a quality > > threshold to reach? That could dramatically increase the number of > > samples while also making it much faster in practice. Nifty! > > Oh, no, I'm _much_ more nifty than that! > > Instead of being very clever, I have a very _stupid_ algorithm, one > that has very hardcoded expectations of exactly what it will see. And > if it doesn't see exactly that, it just fails early. > > I'd post the patch, but I really need to actually _test_ it first, and > I haven't rebooted yet.
ok, will wait with patience :)
i've been using adaptive calibration with great success in user-space, to run benchmarks on multiple boxes with a variable number of lmbench iterations. Once the observable statistical properties of the series of measurements looks valid it stops the test iterations and emits a result. This both makes things faster (more predictable hw/kernel executes certain lmbench tests much faster) and it makes the results more reliable (less noise, better cross-hardware, cross-kernel and cross-test comparisons). I've got a quality threshold (and a max iterations threshold) hardcoded as well.
Ingo
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