-Bryan
On Thu, Feb 04, 1999 at 04:50:04PM -0500, Kris Karas wrote:
> Stephen Foskett wrote:
>
> > There was some discussion of poor PPP performance in the 2.2.x
> > I tried disabling DMA... I tried the other settings with hdparm, too,
>
> There are *two* separate problems, and one other possibliity I'll mention,
> here. One problem is interrupt latency that causes loss of serial bytes. The
> IDE driver is the usual culprit for this one; but you have evidently ruled
> that issue out, leaving some other piece of hardware as the likely culprit.
> Perhaps an ethernet interface? Try looking at /proc/net/interrupts to see if
> anything obvious appears. Any device in polled (PIO) mode is also suspect,
> e.g. a printer port.
>
> Another possibility (particularly if the pppd on the remote end is invoked
> from a shell script) is that some other process is writing to the remote end's
> /dev/ttySx. I was perplexed by these a few years ago until I found some
> obnoxious mail notification programs were dumping output to the raw serial
> line; since pppd had put an entry into utmp linking the tty to my login
> account, the mail program found the line and wrote to it. But that doesn't
> look as though it's your problem either.
>
> The second problem I alluded to is a bona-fide bug in the 2.1/2.2 tcp
> implementation. When the window size shrinks (as is the case when the modem
> buffers lots of serial data), tcp will periodically forget to send packets. I
> almost didn't believe it until I put a tcpdump on both ends of the connection
> and observed the packet loss first hand. But in this scenario, there are no
> errors reported by netstat/ifconfig, as the serial data itself has remained
> intact. I'm still waiting to hear something from the network gurus on this
> one.
>
> Kris
>
>
>
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