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

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Message-ID: <cf54fbb6e05ab86a5c6029eda70012e4.squirrel@www.firstfloor.org>
Date:	Tue, 5 Jul 2011 18:01:36 +0200
From:	"Andi Kleen" <andi@...stfloor.org>
To:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Cc:	"Andi Kleen" <andi@...stfloor.org>,
	"Lin Ming" <ming.m.lin@...el.com>, "Ingo Molnar" <mingo@...e.hu>,
	"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


>
>>   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.

-Andi

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