Messages in this thread | | | Date | Thu, 4 Sep 2008 18:00:37 +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: > > > > i've added them to tip/x86/tsc and merged it into tip/master - if > > there's test success we can merge it into x86/urgent as well and push it > > into v2.6.27. Any objections to that merge route? > > I don't think it's quite that urgent, and wonder what the downside is > of just changing the timeout to 10ms. On 32-bit x86, it was 30ms (I > think) before the merge, so it sounds like 50ms was a bit excessive > even before the whole "loop five times"/ > > So _short_ term, I'd really prefer (a) looping just three times and > (b) looping with a smaller timeout.
ok - sounds very good to me! It's quite late in the cycle so the more commits we can delay to v2.6.28 the better IMHO.
> Long-term, I actually think even 10ms is actually a total waste. I'll > post my trial "quick calibration" code that is more likely to fail > under virtualization or SMM (or, indeed, perhaps even on things like > TMTA CPU's that can have longer latencies due to translation), but > that is really fast and knows very intimately when it succeeds. I just > need to do slightly more testing.
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!
Ingo
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