netdev - Re: Latency difference between fifo and pfifo

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Message-ID: <1323152942.2467.16.camel@edumazet-laptop>
Date:	Tue, 06 Dec 2011 07:29:02 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"John A. Sullivan III" <jsullivan@...nsourcedevel.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Latency difference between fifo and pfifo_fast

Le mardi 06 décembre 2011 à 07:02 +0100, Eric Dumazet a écrit :
> Le lundi 05 décembre 2011 à 23:10 -0500, John A. Sullivan III a écrit :
> > Hello, all.  We are trying to minimize latency on our iSCSI SAN.  The
> > network is entirely dedicated to the iSCSI traffic.  Since all the
> > traffic is the same, would it make sense to change the qdisc for that
> > interface to fifo from the default pfifo_fast or is the latency
> > difference between the two completely negligible? Thanks - John
> 
> A very small difference indeed. How many packets per second are
> expected ? What kind of NIC are you using ?
> 

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



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