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DateSat, 14 Mar 1998 22:02:35 +0100
FromPeter Endeborg <>
SubjectSerial problem => Slow PPP
In the newer kernels I have a realy bad PPP performance. And it is
caused by some
problems in the serial drivers, or interrupt handling.

pme@pescadero$ cat /proc/net/dev /proc/tty/driver/serial
Inter-|   Receive                           |  Transmit
 face |bytes    packets errs drop fifo frame|bytes    packets errs drop
fifo colls carrier multicast
    lo:    2704      43    0    0    0    0     2704       43    0
0    0     0    0    0
  eth0:       0      67    0    0    0    0        0       60    0
0    0     0    0    0
   sl0:       0       0    0    0    0    0      700       13    0
0    0     0    0    0
  ppp0: 1493737     994   90    0    0   87    18605      936    0
0    0     0    0    0
serinfo:1.0 driver:4.24
0: uart:16450 port:3F8 irq:4 tx:0 rx:0
1: uart:16550A port:2F8 irq:3 tx:0 rx:0
2: uart:16550A port:3E8 irq:15 baud:9600 tx:0 rx:0
3: uart:16550A port:2E8 irq:7 baud:57600 tx:18651 rx:1694460 oe:216
RTS|CTS|DTR|DSR|CD
0.13  % of the characters are dropped. This causes a retrasmit timeout,
and that gives
a performance of about 1.8Kbyte/s on a line running at 48kbit/s, and
56700 on the serial link.
(I got a lot more running MSWindos) I have tryed the 2.1.89 kernel with
SMP and without SMP.
I have also tryed to use a other UART, and changed the flowcontrol.
Always the same
speed. The machine is maybe not the most hot one today, but it have been
running a lot better
before. The CPU is a Pentium 120MHz. I have also tryed the unmaskirq on
the disk. I do not
help me at all.


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