From: "Ashton Mills" <amills@iinet.com.au>
To: lartc@vger.kernel.org
Subject: [LARTC] Transmit queue effect?
Date: Mon, 05 May 2003 20:39:33 +0000 [thread overview]
Message-ID: <marc-lartc-105216796431489@msgid-missing> (raw)
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Hey all,
Just a quick question -- does anyone know what impact the txquelen as displayed by ifconfig for a nic really has?
I noticed that, with an HTB qdisc installed (which is what, 128 packets by default?), the txqeuelen is still listed as 100 (ip link list). As an experiment I set off some downloads, and reduced the txqeuelen to 0 (ifconfig eth0 txqueuelen 0) with no effect at all on the stream.
According to man ifconfig:
txqueuelen length
Set the length of the transmit queue of the device. It is useful
to set this to small values for slower devices with a high
latency (modem links, ISDN) to prevent fast bulk transfers from
disturbing interactive traffic like telnet too much.
Even with the default pfifo_fast qdisc all nics start with, reducing or setting the txqueuelen to 0 seems to have no effect. Should it be having an impact, and if not, then why is it there?
I'm optimising a link for certain streams, and using a pfifo with limit 25 on one of the classes. Wondering if any latency saved here is going to be lost further up the chain.
Regards,
Ashton
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