Date: Tue, 01 May 2001 08:30:38 -0700 From: John Merryweather Cooper <jmcoopr@webmail.bmi.net> To: Peter Jeremy <peter.jeremy@alcatel.com.au> Cc: FreeBSD-STABLE Mailing List <freebsd-stable@FreeBSD.ORG> Subject: Re: problem with plip stealing clock Message-ID: <3AEED69E.F6EC1EAD@webmail.bmi.net> References: <3AED84DB.8D241BCF@webmail.bmi.net> <20010501171807.M59150@gsmx07.alcatel.com.au>
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Peter Jeremy wrote: > > 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 suspect transfering between a AMD Duron 700 and an Intel 386SX/20 qualifies . . . :) Couldn't the plip interface arbitrate this though by driving it's "bus" cycle at the pace of the slowest system? I'm sure, in practice, that the rarest use of plip is between two machines of nearly equal CPU speed. Probably, my use is fairly typical. If my damn laptop had a network port, I'd use that--but the Token Ring 16/4 Adapter seems as rare a gold for my ancient AST Premium Exec 386SX/20 . . . :) Probably wouldn't work with FreeBSD anyway . . . bummer. > I did have the problem with PLIP between my 386 laptop and 486 desktop > until I reduced the MTU to 512. Anything "magical" about 512 (or is lower better here). If lower is better, how low can I go (I guess I'll find out). > Have you considered using a PPP link running at 115.2kbps instead? > You will find it a lot more CPU friendly. Yes. Not looking forward to buying yet another single-purpose cable. The null modem I have doesn't seem to do the trick anymore. > Peter > jmc To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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