Packet loss even at low sending rate

Hi all,

I'm trying to evaluate packet forwarding speed of Click. I found that the
router can forward up to 1200kpps (64B packets). But it was strange that at
low packet sending rate (200kpps), the router dropped some packet (0.05%).
Is there any problem with my router configuration or scheduling issue?

* Hardware: CPU Inter Xeon X3210 (quad core at 2.13Ghz), 4GB RAM. (a server
on deterlab)
* Software: Ubuntu8.04 + Click1.8, with PollDevice and multi-thread
enabled.
* Configuration: ./configure --with-linux=/usr/src/linux-2.6.24.7
--enable-ipsec --enable-warp9 --enable-multithread=4
* Installation: sudo click-install --thread=4 site7_router1.click

The router config file is as follows:
==========================
AddressInfo(router1-w1       10.0.1.1        00:15:17:57:c7:4d,
//eth1
            router1-w2       10.0.2.1        00:15:17:57:c7:4f,
//eth3
            router1-w3       10.0.3.1        00:15:17:57:c7:4c,
//eth0
            router1-w4       10.0.4.1        00:15:17:57:c7:4e,
//eth2
            user1-w1         10.0.1.2        00:15:17:57:c8:06,
//eth2
            user2-w2         10.0.2.2        00:15:17:57:c2:1a,
//eth2
            user3-w3         10.0.3.2        00:15:17:57:c6:7a,
//eth2
            user4-w4         10.0.4.2        00:15:17:57:c7:d6);
 //eth2

c1 :: Classifier(12/0806 20/0001,
                 12/0806 20/0002,
                 12/0800,
                 -);
c2 :: Classifier(12/0806 20/0001,
                 12/0806 20/0002,
                 12/0800,
                 -);
c3 :: Classifier(12/0806 20/0001,
                 12/0806 20/0002,
                 12/0800,
                 -);
c4 :: Classifier(12/0806 20/0001,
                 12/0806 20/0002,
                 12/0800,
                 -);

q0 :: ToHost;
q1 :: Queue(10000) -> EtherEncap(0x0800, router1-w1, user1-w1) -> td1 ::
ToDevice(eth1);
q2 :: Queue(10000) -> EtherEncap(0x0800, router1-w2, user2-w2) -> td2 ::
ToDevice(eth3);
q3 :: Queue(10000) -> EtherEncap(0x0800, router1-w3, user3-w3) -> td3 ::
ToDevice(eth0);
q4 :: Queue(10000) -> EtherEncap(0x0800, router1-w4, user4-w4) -> td4 ::
ToDevice(eth2);

rt :: StaticIPLookup(10.0.1.0/32 0, 10.0.1.1/32 0, 10.0.1.255/32 0,
                     10.0.2.0/32 0, 10.0.2.1/32 0, 10.0.2.255/32 0,
                     10.0.3.0/32 0, 10.0.3.1/32 0, 10.0.3.255/32 0,
                     10.0.4.0/32 0, 10.0.4.1/32 0, 10.0.4.255/32 0,
                     10.0.1.0/24 1, 10.0.2.0/24 2, 10.0.3.0/24 3,
                     10.0.4.0/24 4, 0.0.0.0/0 4);
rt[0] -> Discard;
rt[1] -> q1;
rt[2] -> q2;
rt[3] -> q3;
rt[4] -> q4;

pd1 :: PollDevice(eth1) -> c1;
c1[0] -> q0;
c1[1] -> q0;
c1[2] -> Strip(14) -> CheckIPHeader() -> rt;
c1[3] -> Discard;
pd2 :: PollDevice(eth3) -> c2;
c2[0] -> q0;
c2[1] -> q0;
c2[2] -> Strip(14) -> CheckIPHeader() -> rt;
c2[3] -> Discard;
pd3 :: PollDevice(eth0) -> c3;
c3[0] -> q0;
c3[1] -> q0;
c3[2] -> Strip(14) -> CheckIPHeader() -> rt;
c3[3] -> Discard;
pd4 :: PollDevice(eth2) -> c4;
c4[0] -> q0;
c4[1] -> q0;
c4[2] -> Strip(14) -> CheckIPHeader() -> rt;
c4[3] -> Discard;

StaticThreadSched(pd1 0, pd2 1, pd3 2, pd4 3,
                  td2 0, td1 1, td4 2, td3 3);


-- 
Bingyang Liu
Network Architecture Lab, Network Center,Tsinghua Univ.
Beijing, China
Home Page: http://netarchlab.tsinghua.edu.cn/~liuby