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

Am Donnerstag, 18. November 2004 01:01 schrieb Chuck Swiger:
> 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,

GEOM_GATE is my primary goal, and I can remember that when Pavel wrote this 
great feature, he took care about performance and easyly outperformed NFS 
(with 100baseTX AFAIK)

> 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.

I'll do some tests regarding these issues to make sure I'm not suffering from 
ill conditions, but I'm quite sure my testbed's feeling fine. I don't have 
one of these nice managed GigaBit switches, just a x-over cable....

>
> [ ... ]
>
> > - 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.

Of course, but If I connect two GbE cards (wich implies that auto-mdi-X and 
full duplex is mandatory in 1000baseTX mode) I don't expect any UDP packet to 
get lost.
But I'll verify tomorrow.

>
> > - 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

Yep, I know that HZ set to 256 with polling enabled isn't really useful, but I 
don't want to drive my GbE card in polling mode at all, instead I try to 
prevent my machine from spending time doing nothing, so HZ shouldn't be too 
high.

Thank you,

-Harry

> higher HZ is definitely recommmended when you add in jumbo frames and GB
> speeds.