bad PPP Performance (with and without IRQTUNE)

Michael Neuffer (
Wed, 4 Sep 1996 12:47:46 +0200 (MET DST)

Hi Mike,

Would you please forward this to the Linux-kernel list?


I am suffering (among other things) from a horrendously slow PPP performance.

Kernel is 2.0.15 + the last two Linus patches.
MB is P6/200 board with 64MB RAM, AHA2940U, 2IDE drives, IDE CD, NE2000 clone,
SB16 clone card (inactive - another issue) and (optionally) a 16550 UART card.

Symptoms: system is normally lightning FAST. Compiles a complete kernel, on
an Iomega Jaz drive in about 3-4 minutes (distclean, depend, make, zlilo,
modules, modules_install).

PPP is on either Motorola BitSRFR PRO (115,200 on one B channel) or a new USR
Sportster ``33.6 capable'', again, at 115,200.

setserial /dev/cua{1,2} spd_vhi is done on both.

Using CU, either on the built-in UARTs or the external one, serial I/O is FAST.
Hard to measure but flies on the screen, with the ISDN linke visibly faster.

Running PPP (pppd 2.2.0f) disconnects two/three times upon dialup from
either line. Once connection is established, performance is horrendous.
Typically ftp will do 800 bytes/sec on the ISDN line. Less on the

When downloading a file, one can observe the receive LED on the modem/NT
to glow steady and bright with a blip in the other direction every 5
seconds or less. If you abort a transfer, the line remains active for
20-30 seconds (way too long).

Also, while any transfer is occuring, the link is totally dominated by that
transfer; while FTP, if yoy try to type into a telnet session, the aparent
baud rate is less than 1. Way to severe.

The same was confirmed with a P5-90, similarly configured.

I installed IRQTUNE and followed the directions well. Some improvement in
throughput was observe; We now can do almost 1KB/sec on a 64Kbps line.

However, my overpriced P6/200 was transformed into a 386SX, minus the 387,
running over Starlan; Very very slow everything, even when NO serial traffic
was evidenced.

Ethernet traffic on the systems is fine, fast and stable. So it does not
appear to be an IP problem.

Any help will be appreciated.

Please respond to me by email, as I am not in a position to download mailing
list traffic.

Thanx, Simon <>