On Alain Fauconnet's machine (TravelMate 4000M, DX4/100) he had been experiencing a lot of trouble trying to setup a reliable PPP connection over a V34 (28.8kb/s) modem. Symptoms were a lot of "frame with bad fcs" and "frame tossed, reason = 4" messages on the console, and poor overall throughput. Such problems can of course have many causes including wrongly configured modems, bad cables, wrongly configured flow control and many more. After eliminating all those potential reasons, he got help from the Usenet community, more specifically from Theodore Ts'o < tytso@MIT.EDU> and Ciro Cattuto < ciro@stud.unipg.it> .
Theodore pointed out that ``some other device driver (the IDE disk driver is a really bad this way) keeps interrupts off too long, and by the time the serial driver can get control, it's too late. If you can correlate the input overrun messages to disk activity, then you should take a look at man page for the "hdparm" program. In particular, take a look the "-u" option, which is documented for solving the input overrun message, but which causes SEVERE DISK CORRUPTION for some IDE interfaces. Read the man page, including the part of backing up your hard disk first, and decide for yourself if you're willing to risk it.''
Alain followed their advice by installing the hdparm-2.3 program, BACKING UP MY WHOLE DISK and trying (as root) "hdparm -q -u 1 /dev/hda". It did make all the PPP errors disappear. After some time of intensive testing, doing big ftp transfers while keeping my HD busy with big compiles, he decided that this was safe and he added the above command to the end of my /etc/rc.d/rc.local boot script. It has worked flawlessly since then, and Alain now enjoy ftp transfers at 3+ kb/s.
IMPORTANT: this worked for this configuration:
We absolutely cannot guarantee that it will work for any other system/disk/OS version combination. If you try this, DO A FULL BACKUP OF YOUR DISK BEFORE. You have been warned.
HTML document last updated 18 February 1999