Re: IP performance question

[Reco <recoverym4n@gmail.com>]

 Hi.

On Sun, 24 May 2015 10:36:39 +0200
Petter Adsen <petter@synth.no> wrote:

> I've been trying to improve NFS performance at home, and in that
> process i ran iperf to get an overview of general network performance.
> I have two Jessie hosts connected to a dumb switch with Cat-5e. One
> host uses a Realtek RTL8169 PCI controller, and the other has an Intel
> 82583V on the motherboard.
> 
> iperf maxes out at about 725Mbps. At first I thought maybe the switch
> could be at fault, it's a really cheap one, so I connected both hosts
> to my router instead. Didn't change anything, and it had no significant
> impact on the load on the router. I can't try to run iperf on the
> router (OpenWRT), though, as it maxes out the CPU.
> 
> Should I be getting more than 725Mbps in the real world?

A quick test in my current environment shows this:

[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  1.10 GBytes   941 Mbits/sec

Two hosts, connected via Cisco 8-port unmanaged switch, Realtek 8168e
on one host, Atheros Attansic L1 on another.

On the other hand, the same test, Realtek 8139e on one side, but with
lowly Marvell ARM SOC on the other side shows this:

[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   534 MBytes   448 Mbits/sec

So - you can, definitely, and yes, it depends.


> Could there be a driver issue, or some settings that aren't optimal?

Check your iptables rules if any. Especially nat and mangle tables.
Try the same test but use UDP instead of TCP.
Increase TCP window size (those net.core.rmem/wmem sysctls) on both
sides.
Try increasing MTU above 1500 on both sides.
Use crossover cable if everything else fails.


> Unfortunately,
> these are the only two hosts I have with Gbit interfaces (except the
> router), so I can't test with another host.
> 
> Could this be a MB/MiB issue? The iperf man page doesn't say which it
> reports. (Well, it says "Mbit/Mbyte", so I assume it does not mean MiB)

No. (1024*1024*1024 - 1000*1000*1000)/1024/1024 = 70.32.
You can mistake by 70Mbps at most in this scenario, not by 300.


Reco