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Date:      Tue, 01 May 2001 17:18:07 +1000
From:      Peter Jeremy <peter.jeremy@alcatel.com.au>
To:        John Merryweather Cooper <jmcoopr@webmail.bmi.net>
Cc:        FreeBSD-STABLE Mailing List <freebsd-stable@FreeBSD.ORG>
Subject:   Re: problem with plip stealing clock
Message-ID:  <20010501171807.M59150@gsmx07.alcatel.com.au>
In-Reply-To: <3AED84DB.8D241BCF@webmail.bmi.net>; from jmcoopr@webmail.bmi.net on Mon, Apr 30, 2001 at 08:29:31AM -0700
References:  <3AED84DB.8D241BCF@webmail.bmi.net>

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On 2001-Apr-30 08:29:31 -0700, John Merryweather Cooper <jmcoopr@webmail.bmi.net> wrote:
>While using my main workstation as a local FTP for my laptop over plip,
>I noticed that FreeBSD was losing track of time at a prodigious rate.

PLIP receives/transmits each IP packet inside a loop at splhigh().
If either system is slow, or the MTU is too high, the time taken to
transfer each packet can exceed 1 tick - meaning that clock interrupt
is lost.  Other PIO peripherals (ethernet or disk) will aggravate the
problem.

I did have the problem with PLIP between my 386 laptop and 486 desktop
until I reduced the MTU to 512.

Have you considered using a PPP link running at 115.2kbps instead?
You will find it a lot more CPU friendly.

Peter

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