Re: serious networking (em) performance (ggate and NFS) problem

Emanuel Strobl wrote:
[ ... ]
> Tests were done with two Intel GigaBit Ethernet cards (82547EI, 32bit PCI 
> Desktop adapter MT) connected directly without a switch/hub

If filesharing via NFS is your primary goal, it's reasonable to test that, 
however it would be easier to make sense of your results by testing your 
network hardware at a lower level.  Since you're already running portmap/RPC, 
consider using spray to blast some packets rapidly and see what kind of 
bandwidth you max out using that.  Or use ping with -i & -s set to reasonable 
values depending on whether you're using jumbo frames or not.

If the problem is your connection is dropping a few packets, this will show up 
better here.  Using "ping -f" is also a pretty good troubleshooter.  If you 
can dig up a gigabit switch with management capabilities to test with, taking 
a look at the per-port statistics for errors would also be worth doing.  A 
dodgy network cable can still work well enough for the cards to have a green 
link light, but fail to handle high traffic properly.

[ ... ]
> - em seems to have problems with MTU greater than 1500

Have you tried using an MTU of 3K or 7K?

I also seem to recall that there were performance problems with em in 5.3 and 
a fix is being tested in -CURRENT.  [I just saw Scott's response to the list, 
and your answer, so maybe nevermind this point.]

> - UDP seems to have performance disadvantages over TCP regarding NFS which 
> should be vice versa AFAIK

Hmm, yeah...again, this makes me wonder whether you are dropping packets.
NFS over TCP does better than UDP does in lossy network conditions.

> - polling and em (GbE) with HZ=256 is definitly no good idea, even 10Base-2 
> can compete

You should be setting HZ to 1000, 2000, or so when using polling, and a higher 
HZ is definitely recommmended when you add in jumbo frames and GB speeds.

-- 
-Chuck

PS: followup-to set to reduce crossposting...