strange network performance


Subject: strange network performance
From: Charlie Watts (cewatts@frontier.net)
Date: Sun Oct 28 2001 - 17:03:13 MST


I'm seeing strangely slow network performance from YDL. It doesn't seem
YDL specific, but I don't know who else to ask. :-)

In linux, I'm seeing lousy transfer rates to internet sites. 2K/s average.

Here's the whole situation:

iBook 500, YDL2.0.
Connected to internet via D-Link 713P nat/router/wireless thingy, which is
dialing up via 2-channel ISDN.

I see these lousy transfer rates in all of these situations:
   Connected to the 713P via Airport or via 100fdx ethernet.
   In the stock 2.2 YDL2.0 kernel, or in a hand-compiled benh snapshot.

I do not have this problem in Mac OS or Mac OS X. There, I get the normal
10K/s that I'd expect from the ISDN.

But here's the weird part: If I boot Mac-On-Linux, I -also- get the normal
10K/s.

I can be in normal YDL, and fire up an FTP, and get lousy performance.
I can then fire up MOL, and get normal performance from within MOL.

If I dial up directly (not ISDN, but just from the iBook's internal modem)
I get the performance (5-6K) that I would expect.

Any thoughts? My theory is that there is some odd TCP stack timing issue
that the higher latency of the d-link and dialup connection is tickling.

Any suggested sysctls or /proc/mumble things to try changing? Any
troubleshooting ideas?

Because performance is good when booted into Mac OS, even as Mac-On-Linux,
I'm confident that the router/dialup combination is OK. I've also swapped
the 713P out with an identical unit from work - they both work fine on the
LAN, and they are both goofy, but only in Linux, when dialed up.

Slightly different topic: Have you folks seen noflushd? It's -great- on
notebooks for battery life or on desktops that you want to make quieter
when they aren't in use. Not perfect, but great.

http://noflushd.sourceforge.net/

It basically spins down hard disks when they aren't in use - but then it
also prevents linux from flushing buffers and waking the disks back up.
Any sync write will wake the disks back up, and it wakes them up
periodically to do allow a flush ...

If you use it, you might also want to change /etc/cron.d/kmod to run
hourly instead of every five minutes, and be sure to change /etc/syslog to
NOT do sync writes (prepend the logfile names with a dash, like
"-/var/log/messages") ...

-- 
Charlie Watts
cewatts@frontier.net
Frontier Internet, Inc.
http://www.frontier.net/



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