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 | |
* 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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