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

[liu.yulou at zte.com.cn]

thank you for the answer. there are two questions :

1.   is it possible to copy data directly from the kernel buffer to the 
final buffer (  which I want the date kept  in) ? 
2. or is there any way that programmer can modify the address of the user 
buffer directly? 

thank you.



Yulou





"Gianluca Varenni" <gianluca.varenni at cacetech.com> 
发件人:  winpcap-users-bounces at winpcap.org
2010-09-21 07:45
请答复 给
winpcap-users at winpcap.org


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






Two notes: 
 
1. if the objective is dumping the packets to disk, then the bottleneck is 
mostly the disk. 
2. checksum offloading does not play any role in packet capture. It plays 
a role when packets have to be processed by the TCP/IP stack (because the 
validation is done in hardware rather software). But when you do packet 
capture, you don't care about that. In fact I suggested to totally disable 
TCP/IP from the NIC where you capture the packets from.
 
GV

From: "Fish" (David B. Trout) 
Sent: Sunday, September 19, 2010 4:44 AM
To: winpcap-users at winpcap.org 
Subject: Re: [Winpcap-users] About the packets loss ,what is the 
bottleneck ?

There are other factors as well:
 
1.       Number of processors and processor speed.
2.       Amount of RAM
3.       Operating system workload
4.       Network Adapter Task Offloading capability (esp. checksum 
offloading)
5.       Speed of disk subsystem
 
On an modern fast quad-core system that is relatively idle (has no other 
work to do) with lots of RAM and a high performance multi-disk RAID-0 
array and with checksum offloading enabled in the adapter, it should be 
entirely possible to capture a gigabit speed without packet loss.
 
If your system is an overtaxed (busy) single processor system with only an 
average amount of RAM and an average speed non-RAID disk subsystem 
however, then you’re very likely going to experience significant packet 
loss beyond about 480 Mbps.
-- 
  "Fish"  (David B. Trout) 
    fish at softdevlabs.com
 
From: winpcap-users-bounces at winpcap.org 
[mailto:winpcap-users-bounces at winpcap.org] On Behalf Of yulou liu
Sent: Sunday, September 19, 2010 12:50 AM
To: winpcap-users at winpcap.org
Subject: [Winpcap-users] About the packets loss , what is the bottleneck ?
Importance: High
 

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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