[Winpcap-users] About the packets loss , what is the bottleneck ?

[yulou liu]

There is still the question about packets loss.

According to the essay  ' Profiling and Optimization of Software-Based
Network-Analysis Applications' ,    every packet is copied twice in the main
memory before reaching the user.  In order to reduce the cost of CPU and the
bus occupying of the SDRAM of pc,   is it possible to copy data directly
from the kernel buffer to the final buffer ,  which I want the date kept  in
?

Here is another idea ---  allocate several different user buffers , once a user
buffer is fulled , then let the next user buffer to save the new datas from
kernel buffer.  Meanwhile copy datas from the first user buffer to disk
(assume that the hard disk write rate is fast enough).  Is this idea work
with the winpcap ?


Thank you!

==============================================================

Q1: tough question to answer, as it depends on a number of factors. What is
the average packet size? Are you just counting the packets, or dumping them
to disk/DB/...? Do you see packet drops in the pcap_stats?
Q2: I will need to run some tests on this. Do you have some minimal sample
code that shows the issue?
Q3: Yes, *if* the NIC (and NIC driver) are not dropping packets themselves.

Did you disable any protocol bound to the NIC where you receive all these
packets?

Have a nice day
GV




From: yulou liu
Sent: Wednesday, August 25, 2010 11:08 AM
To: winpcap
Subject: [Winpcap-users] About the packets loss , what is the bottleneck ?


I'm using winpcap to capture datas from FPGA board via 1G Ethernet
connection(directly connected).
the FPGA is configed to send data at a special rate. With the fpga sending
rate increases,especially above 500Mbps, it sometimes loss packets.

Q1:  Is it possible to totally avoid packets loss by optimism the code?  I
want to collect datas at speed 614Mbps without packet loss (collecting all
datas

last about 1 minutes). My workstations features with 2 Xeon CPU (each has
4core), DDR3 SDRAM, 1 G onboard  netcard.  Which part is the most probably
bottleneck ?

Q2: As a test ,  I found the pcap_next_ex() can't get any packets  when the
user buffer is set over 64 MB,  what does it happen ?

Q3: if the Kernel buffer's size is 16MB , then the first 16Mb packets from
fpga won't be lost,  so ,  if I set the kernel buffer as 128MB ,  then at
least

the first coming 128MB data from FPGA won't be lost either ?  but I found
When I set the kernel buffer bigger than 100 MB, the packets drops is
getting

worse.


Thanks a lot!
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