network slowdown?

From: Howard Chu
Date: Wed Jul 27 2005 - 03:46:42 EST

I just recently compiled the kernel for my x86_64 machine
(Asus A8V motherboard); was previously running a SuSE-compiled 2.6.8
kernel (SuSE 9.2 distro). I'm now seeing extremely slow throughput on
the onboard Yukon (Marvell) ethernet interface, but only in certain
conditions. Going back to the 2.6.8 kernel shows no slowdown.

I have a few machines connected to a Linksys 5 port 10/100 hub. There
is also a Linksys WRT54G wireless router on this hub. When doing a raw ftp transfer of a large (600MB) file (using a Windows XP client to do a
GET) with both machines plugged into the hub, I see transfer rates only
as high as 1MB/sec initially, which quickly degrades to ~200KB/sec over a span of 20-30 seconds. Going the opposite direction, a PUT runs at a steady 7.5MB/sec.

If I unplug the Windows client and just connect via the wireless network, I see GETs run a steady 2.8MB/sec and PUTs run a steady 3.2MB/sec, which is about the same as I saw with the 2.6.8 kernel, so that all appears normal. (But it's still odd, that adding one hop like this avoids the throughput degradation.)

I don't see any collisions or any other errors on the ifconfig statistics, just a very slow transmit rate. Does anyone recognize this symptom? Any suggestions on tunables to tweak, etc.? (Please cc: me directly when replying, thanks.)

-- Howard Chu
Chief Architect, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc
OpenLDAP Core Team http://www.openldap.org/project/
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