[Gllug] Observed speed of gigabit ethernet only about 1/4 or 1/5 of advertised

[Richard Jones]

Hi, I've just got a new gigabit ethernet switch to replace my ancient
10 Mbps home switch.  The old switch easily maxed out at 10 Mbps.

With the other ports on the switch idle and two machines connected
through gigabit ethernet, I'm seeing 220 Mbps with ssh.  That's about
a quarter of what I'd expect to be the theoretical maximum.
Surprisingly with ttcp it's slower -- 170 Mbps, or about one fifth of
the theoretical max.  With UDP it's little better -- 195 Mbps.

I wonder if someone can suggest from the description below where the
weak point is likely to be in this setup.  Crappy on-board ethernet?
SoHo switch?  PCI bus or processor speeds?  Or does everyone with
gigabit ethernet only see a fraction of the advertised throughput?

  Machine A:

    eth0: VIA Networking Velocity Family Gigabit Ethernet Adapter
    AMD Athlon(tm) 64 Processor 3200+ (2043.109 MHz)
    2 GB RAM

  Machine B:

    eth0: forcedeth.c: subsystem: 010f1:2915 bound to 0000:00:08.0
    Quad AMD Opteron(tm) Processor 2220 (2814 MHz)
    4 GB RAM

  Switch:

    Netgear GS105 5-port Gigabit Ethernet Switch

# ttcp -t -s -p 631 -n 100000 -l 65536 -f m 192.168.2.4
ttcp-t: buflen=65536, nbuf=100000, align=16384/0, port=631  tcp  -> 192.168.2.4
ttcp-t: socket
ttcp-t: connect
ttcp-t: 6553600000 bytes in 293.12 real seconds = 170.58 Mbit/sec +++
ttcp-t: 100000 I/O calls, msec/call = 3.00, calls/sec = 341.15
ttcp-t: 0.0user 12.9sys 4:53real 4% 0i+0d 0maxrss 0+17pf 6461+124csw

# ttcp -t -s -p 631 -n 100000 -u -f m 192.168.2.4
ttcp-t: buflen=8192, nbuf=100000, align=16384/0, port=631  udp  -> 192.168.2.4
ttcp-t: socket
ttcp-t: 819200000 bytes in 31.99 real seconds = 195.40 Mbit/sec +++
ttcp-t: 100006 I/O calls, msec/call = 0.33, calls/sec = 3126.59
ttcp-t: 0.0user 1.6sys 0:31real 5% 0i+0d 0maxrss 0+3pf 14162+10csw

Rich.

-- 
Richard Jones
Red Hat
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