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Date: Wed, 6 Jul 2011 11:35:01 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Andi Kleen <andi@firstfloor.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Lin Ming <ming.m.lin@intel.com>,
        Stephane Eranian <eranian@google.com>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
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Subject: Re: [PATCH 1/4] perf, x86: Add Intel Nehalem/Westmere uncore pmu
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* Andi Kleen <andi@firstfloor.org> wrote:

> 
> >
> >>   But it's not strictly required I would say,
> >> 44(?) bits are probably enough for near all use cases.
> >
> > 44bits is in the hours range for pure cycle counts, which is 
> > so-so. I bet you're going to be very annoyed when you find your 
> > counters are wrecked after your 5 hour test run finishes.
> 
> For these kinds of long running measurements you usually care about 
> ratios, not absolutes. Some infrequent wrapping should not 
> substantially change. those.

That's just empty blathering - those who *do* take a look at 
long-running absolute values obviously care.

There's absolutely no reason to be sloppy here - this needs to be 
implemented correctly.

Thanks,

	Ingo