freebsd stable - Sep 2016 - LAGG and Jumbo Frames

> Everything on physical Ethernet has support for it Including the LAN 
> interface of Firewall, and talks to it just fine over a single interface
with
> Jumbo frames enabled.
Well, before you get too carried away, try this:

1) Run a ttcp test between a pair of local hosts using the exiting 
jumboframes (pick two that you expect high volume traffic between).

2) Run the same test, but with the default MTU.

If you don't see a very visible difference in throughput (e.g. >15%),
it's
not worth the hassle.

Just as a datapoint, we're running 10-gigE off some low-end Supermicro 
boxes with 10.3-RELEASE.  Using the default MTU we're getting > 750 MB/s 
TCP throughput.  I can't believe that you won't be able to fully
saturate
a 1 Gb/s link running the default MTU on anything with more oomph than a 
dual-core 32-bit Atom.

IOW, don't micro-optimize.  Life's too short ...

--lyndon

On Mon, Sep 19, 2016 at 02:28:56PM -0700, Lyndon Nerenberg wrote:
> > Everything on physical Ethernet has support for it Including the LAN 
> > interface of Firewall, and talks to it just fine over a single
interface with
> > Jumbo frames enabled.
> 
> Well, before you get too carried away, try this:
> 
> 1) Run a ttcp test between a pair of local hosts using the exiting 
> jumboframes (pick two that you expect high volume traffic between).
> 
> 2) Run the same test, but with the default MTU.
> 
> If you don't see a very visible difference in throughput (e.g.
>15%), it's
> not worth the hassle.
> 
> Just as a datapoint, we're running 10-gigE off some low-end Supermicro 
> boxes with 10.3-RELEASE.  Using the default MTU we're getting > 750
MB/s
> TCP throughput.  I can't believe that you won't be able to fully
saturate
> a 1 Gb/s link running the default MTU on anything with more oomph than a 
> dual-core 32-bit Atom.
> 
> IOW, don't micro-optimize.  Life's too short ...
May be surprised, but jumbo frames can degrade performance for not
direct connected host, i.e. multiple switch between host:


[hostA]=[SW1]=[SW2]=[SW3]=[hostB]

This is because RTT of this link for jumbo frames higher 1500 bytes
frame for store-and-forward switch chain.