From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Ashton Mills" Date: Mon, 05 May 2003 20:39:33 +0000 Subject: [LARTC] Transmit queue effect? MIME-Version: 1 Content-Type: multipart/mixed; boundary="----=_NextPart_000_000E_01C3139A.410CB8F0" Message-Id: List-Id: To: lartc@vger.kernel.org This is a multi-part message in MIME format. ------=_NextPart_000_000E_01C3139A.410CB8F0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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 ------=_NextPart_000_000E_01C3139A.410CB8F0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Hey all,

Just a quick question -- does anyone know what impact the txquelen as displayed = by ifconfig=20 for a nic really has?

I noticed that, with an HTB qdisc = installed (which=20 is what, 128 packets by default?), the txqeuelen is still listed as 100 = (ip link=20 list). As an experiment I set off some downloads, and reduced the = txqeuelen to 0=20 (ifconfig eth0 txqueuelen 0) with no effect at all on the = stream.

According to man ifconfig:

txqueuelen=20 length
          &nb= sp;  =20 Set the length of the transmit queue of the device. It is=20 useful
          &nb= sp;  =20 to set this to small values for slower devices =20 with a =20 high
           = ;  =20 latency (modem links, ISDN) to prevent fast bulk transfers=20 from
           = ;  =20 disturbing interactive traffic like telnet too much.

Even with the default pfifo_fast qdisc = all nics=20 start with, reducing or setting the txqueuelen to 0 seems to have = no=20 effect. Should it be having an impact, and if not, then why is it=20 there?

I'm optimising a link for certain = streams, and=20 using a pfifo with limit 25 on one of the classes. Wondering = if any=20 latency saved here is going to be lost further up the = chain.

Regards,

Ashton

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