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Date: Fri, 08 Mar 2002 10:50:53 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Jamie Lokier <lk@tantalophile.demon.co.uk>
CC: linux-kernel@vger.kernel.org, Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Terje Eggestad <terje.eggestad@scali.com>,
        Ben Greear <greearb@candelatech.com>,
        Davide Libenzi <davidel@xmailserver.org>,
        george anzinger <george@mvista.com>
Subject: Re: gettimeofday() system call timing curiosity
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Jamie Lokier wrote:

> 
> On my laptop, the median of rdtsc+gettimeofday+rdtsc times is 470 cycles
> for most runs of 1000, but is occasionally 453 cycles.
> 


What that indicates to me is that 1000 is way too small of a sample. 
You're only talking a difference of 17,000 cycles, which could -- 
especially with cache effects -- easily be the time spent in an 
interrupt handler.

	-hpa



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