netdev - Re: [PATCH v15 ] net/veth/XDP: Line-rate packet forwarding in kernel

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Date:   Wed, 4 Apr 2018 08:16:04 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     "Md. Islam" <mislam4@...t.edu>
Cc:     netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
        David Ahern <dsahern@...il.com>, stephen@...workplumber.org,
        agaceph@...il.com, Pavel Emelyanov <xemul@...nvz.org>,
        Eric Dumazet <edumazet@...gle.com>,
        alexei.starovoitov@...il.com, brouer@...hat.com
Subject: Re: [PATCH v15 ] net/veth/XDP: Line-rate packet forwarding in
 kernel

On Sun, 1 Apr 2018 20:47:28 -0400 Md. Islam" <mislam4@...t.edu> wrote:

> [...] More specifically, header parsing and fib
> lookup only takes around 82 ns. This shows that this could be used to
> implement linerate packet forwarding in kernel.

I cannot resist correcting you...

You didn't specify the link speed, but assuming 10Gbit/s, then the
linerate is 14.88Mpps, which is 67.2 ns between arriving packets. Thus,
if the lookup cost is 82 ns, thus you cannot claim linerate performance
with these numbers.

Details:

This is calculated based on the the minimum Ethernet frame size
84-bytes, see https://en.wikipedia.org/wiki/Ethernet_frame for why this
is the minimum size.

10*10^9/(84*8) = 14,880,952 pps
1/last*10^9    = 67.2 ns

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer