From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: Latency difference between fifo and pfifo_fast Date: Tue, 06 Dec 2011 07:29:02 +0100 Message-ID: <1323152942.2467.16.camel@edumazet-laptop> References: <30c2e9e0-4208-4c19-9e43-31f95e13575d@jasiiieee> <1323151377.2467.13.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: netdev@vger.kernel.org To: "John A. Sullivan III" Return-path: Received: from mail-ee0-f46.google.com ([74.125.83.46]:56790 "EHLO mail-ee0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932822Ab1LFG3H (ORCPT ); Tue, 6 Dec 2011 01:29:07 -0500 Received: by eeaq14 with SMTP id q14so2557822eea.19 for ; Mon, 05 Dec 2011 22:29:06 -0800 (PST) In-Reply-To: <1323151377.2467.13.camel@edumazet-laptop> Sender: netdev-owner@vger.kernel.org List-ID: Le mardi 06 d=C3=A9cembre 2011 =C3=A0 07:02 +0100, Eric Dumazet a =C3=A9= crit : > Le lundi 05 d=C3=A9cembre 2011 =C3=A0 23:10 -0500, John A. Sullivan I= II a =C3=A9crit : > > Hello, all. We are trying to minimize latency on our iSCSI SAN. T= he > > network is entirely dedicated to the iSCSI traffic. Since all the > > traffic is the same, would it make sense to change the qdisc for th= at > > interface to fifo from the default pfifo_fast or is the latency > > difference between the two completely negligible? Thanks - John >=20 > A very small difference indeed. How many packets per second are > expected ? What kind of NIC are you using ? >=20 To really remove a possible source of latency, you could remove qdisc layer... ifconfig eth2 txqueuelen 0 tc qdisc add dev eth2 root pfifo tc qdisc del dev eth2 root