netdev - Re: Unexcepted latency (order of 100-200 ms) with TCP (packet receive)

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Message-Id: <20070427031757.513f6ad7.billfink@mindspring.com>
Date:	Fri, 27 Apr 2007 03:17:57 -0400
From:	Bill Fink <billfink@...dspring.com>
To:	"Ilpo =?ISO-8859-1?Q?J=E4rvinen" ?= <ilpo.jarvinen@...sinki.fi>
Cc:	Chuck Ebbert <cebbert@...hat.com>, Netdev <netdev@...r.kernel.org>
Subject: Re: Unexcepted latency (order of 100-200 ms) with TCP (packet
 receive)

On Thu, 26 Apr 2007, Ilpo Järvinen wrote:

> On Thu, 26 Apr 2007, Chuck Ebbert wrote:
> 
> > Ilpo Järvinen wrote:
> > > ...I'm unsure how to continue the investigation from this point onward 
> > > and asking for ideas/suggestions or how to rule out more possibilities... 
> > > Or is there some knob which I don't know of that should be toggled or 
> > > something, is 2.6 network stack expected to behave this way?
> > > 
> > 
> > Try a different network adapter.
> 
> Hmm, I thought I had already done this but I just noticed that it is so 
> that the adapter was still the same as the other host has two adapter (now 
> that I look again). I'll give it a try tomorrow to see if using the 
> another adapter makes any difference.
> 
> > Try turning off hardware TSO offload:
> >   ethtool -K ethX tso off
> 
> # ethtool -K eth0 tso off
> Cannot set device tcp segmentation offload settings: Operation not 
> supported

Could the delays be caused by Ethernet PAUSE frames (which might not
be rquired at the slower 10FD but might at 100)?  TX and RX pause
control settings (check with "ethtool -a") might be different between
the 2.4 and 2.6 kernels.

Also check things like net.core.netdev_max_backlog and ifconfig
txqueuelen settings.  And check "ethtool -S", "netstat -s", and
ifconfig error counters.

						-Bill
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