tap device speed

[Stephen Hemminger]

On Mon, 2 Oct 2023 21:13:03 +0200
Antonio Di Bacco <a.dibacco.ks at gmail.com> wrote:

> I'm doing a test where we have a couple of tap devices, the two
> devices are seen by testpmd that is setup in forward mode.
> 
> On the linux side, the two tap devices are confined in different
> network namespaces and in one namespace we have an iperf server while
> on the other namespace the iperf client sending either UDP or TCP.
> 
> I expected a bandwidth in the range of few gpbs while the actual
> measured bandwidth is a few gigabits.
> 
> I suppose I need to configure the tap devices with optimized
> parameters but I don't know where to look for advice.
> 
> If I try to use the loopback interface I can get something 40 gbps
> with a command like this:
> 
> iperf -c 127.0.0.1 -u -i 1 -b 40g -t 10 -l 40000
> 
> .

Sorry TAP device is inherently slow. It requires copies to/from Linux
kernel. You are doing well if you get 1 million packets per second.

One thing to check is that checksum is not being done twice.