[tcpdump-workers] Huge latency increase libpcap-1.4.0 -> libpcap-1.5.3

[Steve Bourland]

I have some programs that suffered terrible performance degradation when 
moving from Ubuntu 12.04 to Ubuntu 14.04.  Originally I blamed Ubuntu 
14.04 for the performance hit and simply stuck with 12.04, however when I 
updated libpcap to support hardware timestamps, the performance degraded 
again.  I then reduced the problem to a program that simple returned ICMP 
ECHO replies when requests were received.  Under 12.04, this program works 
very well (with reported responses from ping of under 500 usec), however, 
if I point the libpcap.so files to the downloaded version 1.5.3 
(originally tested with 1.6.2 and problem seen there as well), the 
response times jump to sometimes over 100 msec.  Similarly, if I run the 
program on Ubuntu 14.04 I see response times well over 10 msec (and 
actually miss many requests).  If I simply replace the links to 
libpcap.so.1.5.3 with links to libpcap.so.1.4.0 the responses return to 
sub 300 usec.  Is this behavior expected?  Do I need to redo my pcap 
handle setup if moving from libpcap-1.4.0 to libpcap-1.5.3 (or 
libpcap-1.6.2)?  Any guidance is greatly appreciated.  Any troubleshooting 
I can do to help out?
                                        Thanks,
                                          Steve
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