[Winpcap-users] Problem with dropped packets

[Morrow, Carson]

I'm using winpcap to interface with some test equipment that
communicates over an 100 Mb Ethernet connection (directly connected, no
switch or hub). The test equipment centers around an FPGA, and I control
the code on the FPGA. Most of the time, the test equipment is sending
status information (two 60 B packets/s), but occasionally it will
transfer the data it has collected, in response to a specific packet
from the computer. It's up to 64 MB of data, transferred in up to
2097152 packets (for the full 64 MB). I want to transfer the data as
quickly as possible, but I'm having trouble with packets getting
dropped.

 

I'm using pcap_next_ex in a separate thread from the UI thread. I've
adjusted the kernel buffer using pcap_setbuff, although I understand now
that increasing that buffer only delays the onset of the dropped
packets. I only capture the minimum portion of the packet required (60
B). I've tried adjusting the read timeout, turning off promiscuous mode,
and adjusting the kernel copy size, without the improvement I'm looking
for. The thread calling pcap_next_ex does very little else when
receiving the test data, and right now I just have it checking the
packet sequence number (so I can tell if it's dropping packets) and
incrementing a counter (the UI is updated with the counter value by the
separate UI thread). I tried using pcap_stats_ex to get data on the
actual number of packets dropped, but it shows "0" for the different
packet drop counts.

 

Right now, I'm seeing a few dropped packets even when sending at ~60,000
packets/s. This is with promiscuous mode on, a 500 ms read timeout, a 4
MB kernel buffer, and the min copy size adjusted anywhere from the
default (16 kB, I believe) to 1 MB. I test using the release version of
the software, compiled with optimizations for speed. I'm running winpcap
4.1.2 on XP on a reasonably recent laptop (Core 2 Duo, 2 GB RAM). From
reading through the archives here, I'm certain winpcap can provide
better performance than this.

 

I can provide code if it helps.

 

Thanks,

 

Carson

 

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