Major performance hit with ToS setting

[Bjoern A. Zeeb]

On 24. May 2012, at 22:55 , Kevin Oberman wrote:

> When we set the ToS bits for less than best effort (also called
> scavenger) on packets (ToS=32), performance on FreeBSD 8.2 is
> terrible. It was as good as best effort on FreeBSD 7.3 (assuming no
> congestion). I will look into what 9 does, but does anyone have an
> idea of why 8.2 behaves so badly when ToS is set to 32?
> Here is an example of what happens to performance:
> nuttcp with ToS=0:
> 622.5000 MB /   1.00 sec = 5221.7570 Mbps
> 623.3125 MB /   1.00 sec = 5228.5883 Mbps
> 624.0000 MB /   1.00 sec = 5234.4495 Mbps
> 
> With ToS=32 (0x20):
> 0.3750 MB /   1.00 sec =    3.1457 Mbps
> 0.5000 MB /   1.00 sec =    4.1942 Mbps
> 0.5000 MB /   1.00 sec =    4.1942 Mbps
> 
> This is,of course, on a 10G interface. On 7.3 there is little
> difference between the two. We are using cubic CC on the 8.2 system.

This looks like a different problem than just TOS.  I assume however
that not setting the TOS you get the same as expected performance?

Which NIC?

/bz

-- 
Bjoern A. Zeeb                                 You have to have visions!
   It does not matter how good you are. It matters what good you do!