[Click] HELP:ToDevice element too slow,what's the problem???????

[shule ney]

Hi all:
I got a weird problem when I'm using udpgen.click, below is my udpgen.click:

// UDPGen($device, $rate, $limit, $seth, $sip, $sport, $deth, $dip, $dport);
//
//	$device		name of device to generate traffic on
//	$rate		rate to generate traffic (packets/s)
//	$limit		total number of packets to send
//      $size		bytes per packet
//	$seth		source eth addr
//	$sip		source ip addr
//	$sport		source port
//      $deth		destination eth addr
//	$dip		destination ip addr
//	$dport		destination port

elementclass UDPGen {
  $device, $rate, $limit, $size,
  $seth, $sip, $sport, $deth, $dip, $dport |

  source :: FastUDPSource($rate, $limit, $size, $seth, $sip, $sport,
                                                $deth, $dip, $dport);
 * //**pd :: PollDevice($device) -> ToHost;* //commented out
  source -> td :: ToDevice($device);
}

// create a UDPGen

u :: UDPGen(eth1, 1800000, 8200000, 64,
	    00:e0:29:05:e2:d4, 2.0.0.2, 1234,
	    00:c0:95:e2:09:14, 1.0.0.2, 1234

and when I start it, I got messages as below:
*ToDevice eth1 is full, packet delayed*
and when I check the calls in todevice,it shows:
1172 packets held
0 packets dropped
92828616 hard start xmit
1212233322 device busy returns
92827444 packets sent
1214691606 calls to run_task()
92828656 pulls

The sending speed is only about 750Kpps, I remember before is around
1.7Mpps(I reformatted the disk and reinstall Linux). So what could be the
problem??Thanks very much for your help, I'll appreciate it.

Best
shule