linux-kernel - Re: [PATCH 1/4] perf, x86: Add Intel Nehalem/Westmere uncore pmu

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Message-ID: <20110706093501.GA11969@elte.hu>
Date:	Wed, 6 Jul 2011 11:35:01 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Lin Ming <ming.m.lin@...el.com>,
	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] perf, x86: Add Intel Nehalem/Westmere uncore pmu


* Andi Kleen <andi@...stfloor.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
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