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

Dear best guys,

I really love 5.3 in many ways but here're some unbelievable transfer rates, 
after I went out and bought a pair of Intel GigaBit Ethernet Cards to solve 
my performance problem (*laugh*):

(In short, see *** below)

Tests were done with two Intel GigaBit Ethernet cards (82547EI, 32bit PCI 
Desktop adapter MT) connected directly without a switch/hub and "device 
polling" compiled into a custom kernel with HZ set to 256 and 
kern.polling.enabled set to "1":

LOCAL:
(/samsung is ufs2 on /dev/ad4p1, a SAMSUNG SP080N2)
 test3:~#7: dd if=/dev/zero of=/samsung/testfile bs=16k
 ^C10524+0 records in
 10524+0 records out
 172425216 bytes transferred in 3.284735 secs (52492882 bytes/sec)
->
                                                 ^^^^^^^^ ~ 52MB/s
NFS(udp,polling):
(/samsung is nfs on test3:/samsung, via em0, x-over, polling enabled)
 test2:/#21: dd if=/dev/zero of=/samsung/testfile bs=16k
 ^C1858+0 records in
 1857+0 records out
 30425088 bytes transferred in 8.758475 secs (3473788 bytes/sec)
->                                                ^^^^^^^ ~ 3,4MB/s

This example shows that using NFS over GigaBit Ethernet decimates performance 
by the factor of 15, in words fifteen!

GGATE with MTU 16114 and polling:
 test2:/dev#28: ggatec create 10.0.0.2 /dev/ad4p1
 ggate0
 test2:/dev#29: mount /dev/ggate0 /samsung/
 test2:/dev#30: dd if=/dev/zero of=/samsung/testfile bs=16k
 ^C2564+0 records in
 2563+0 records out
 41992192 bytes transferred in 15.908581 secs (2639594 bytes/sec)
->                                                 ^^^^^^^ ~ 2,6MB/s

GGATE without polling and MTU 16114:
 test2:~#12: ggatec create 10.0.0.2 /dev/ad4p1
 ggate0
 test2:~#13: mount /dev/ggate0 /samsung/
 test2:~#14: dd if=/dev/zero of=/samsung/testfile bs=128k
 ^C1282+0 records in
 1281+0 records out
 167903232 bytes transferred in 11.274768 secs (14891945 bytes/sec)
->                                                  ^^^^^^^^ ~ 15MB/s
.....and with 1m blocksize:
 test2:~#17: dd if=/dev/zero of=/samsung/testfile bs=1m
 ^C61+0 records in
 60+0 records out
 62914560 bytes transferred in 4.608726 secs (13651182 bytes/sec)
->                                                ^^^^^^^^ ~ 13,6MB/s

I can't imagine why there seems to be a absolute limit of 15MB/s that can be 
transfered over the network
But it's even worse, here two excerpts of NFS (udp) with jumbo Frames 
(mtu=16114):
 test2:~#23: mount 10.0.0.2:/samsung /samsung/
 test2:~#24: dd if=/dev/zero of=/samsung/testfile bs=1m
 ^C89+0 records in
 88+0 records out
 92274688 bytes transferred in 13.294708 secs (6940708 bytes/sec)
->                                                 ^^^^^^^ ~7MB/s
.....and with 64k blocksize:
 test2:~#25: dd if=/dev/zero of=/samsung/testfile bs=64k
 ^C848+0 records in
 847+0 records out
 55508992 bytes transferred in 8.063415 secs (6884055 bytes/sec)

And with TCP-NFS (and Jumbo Frames):
 test2:~#30: mount_nfs -T 10.0.0.2:/samsung /samsung/
 test2:~#31: dd if=/dev/zero of=/samsung/testfile bs=64k
 ^C1921+0 records in
 1920+0 records out
 125829120 bytes transferred in 7.461226 secs (16864403 bytes/sec)
->                                                 ^^^^^^^^ ~ 17MB/s

Again NFS (udp) but with MTU 1500:
 test2:~#9: mount_nfs 10.0.0.2:/samsung /samsung/
 test2:~#10: dd if=/dev/zero of=/samsung/testfile bs=8k
 ^C12020+0 records in
 12019+0 records out
 98459648 bytes transferred in 10.687460 secs (9212633 bytes/sec)
->                                                 ^^^^^^^ ~ 10MB/s
And TCP-NFS with MTU 1500:
 test2:~#12: mount_nfs -T 10.0.0.2:/samsung /samsung/
 test2:~#13: dd if=/dev/zero of=/samsung/testfile bs=8k
 ^C19352+0 records in
 19352+0 records out
 158531584 bytes transferred in 12.093529 secs (13108794 bytes/sec)
->                                                  ^^^^^^^^ ~ 13MB/s

GGATE with default MTU of 1500, polling disabled:
 test2:~#14: dd if=/dev/zero of=/samsung/testfile bs=64k
 ^C971+0 records in
 970+0 records out
 63569920 bytes transferred in 6.274578 secs (10131346 bytes/sec)
->                                                ^^^^^^^^ ~ 10M/s


Conclusion:

***

- It seems that GEOM_GATE is less efficient with GigaBit (em) than NFS via TCP 
is.

- em seems to have problems with MTU greater than 1500

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

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

- NFS over TCP with MTU of 16114 gives the maximum transferrate for large 
files over GigaBit Ethernet with a value of 17MB/s, a quarter of what I'd 
expect with my test equipment.

- overall network performance (regarding large file transfers) is horrible

Please, if anybody has the knowledge to dig into these problems, let me know 
if I can do any tests to help getting ggate and NFS useful in fast 5.3-stable 
environments.

Best regards,

-Harry