netdev - Re: Latency difference between fifo and pfifo

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Message-ID: <1323161496.2448.7.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Tue, 06 Dec 2011 09:51:36 +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 03:39 -0500, John A. Sullivan III a écrit :

> > ifconfig eth2 txqueuelen 0
> > tc qdisc add dev eth2 root pfifo
> > tc qdisc del dev eth2 root
> > 
> > 
> > 
> > 
> Really? I didn't know one could do that.  Thanks.  However, with no
> queue length, do I have a significant risk of dropping packets? To
> answer your other response's question, these are Intel quad port e1000
> cards.  We are frequently pushing them to near line speed so
> 1,000,000,000 / 1534 / 8 = 81,486 pps - John

You can remove qdisc layer, since NIC itself has a TX ring queue

(check exact value with ethtool -g ethX)

# ethtool -g eth2
Ring parameters for eth2:
Pre-set maximums:
RX:		4078
RX Mini:	0
RX Jumbo:	0
TX:		4078
Current hardware settings:
RX:		254
RX Mini:	0
RX Jumbo:	0
TX:		4078      ---- HERE ----



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