On Fri, 14 Nov 2014, Guy Harris wrote:
On Nov 14, 2014, at 2:08 PM, Steve Bourland <sbourl...@swri.edu> wrote:
On Fri, 14 Nov 2014, Guy Harris wrote:
On Nov 14, 2014, at 1:17 PM, Steve Bourland <sbourl...@swri.edu> wrote:
I have some programs that suffered terrible performance degradation
when moving from Ubuntu 12.04 to Ubuntu 14.04.
Are those programs capturing and processing network traffic, are they
sending packets and expecting to receive a response, or are they doing
something else?
They are essentially servers, listening for specific packets and then
building and sending the appropriate reply to the client.
OK, that's the same case, from the point of view of using libpcap, as
the client case of sending packets and expecting to receive a response.
Is the performance issue one of high latency or of dropped packets
when capturing?
Sorry, the main concern I have is high latency,
As I suspected.
What timeout are you specifying with pcap_open_live() or
pcap_set_timeout()?
In the test program I am using 1 msec as the timeout for
pcap_open_live...but then have a selectable fd and am using a select
call to let me know when a packet arrives.
Well, 1 ms is the smallest that the timeout can get.
For PF_PACKET sockets, which are what libpcap uses on Linux, the
TPACKET_V3 mechanism, which is the default in 1.5.0 and later and which
works better for the packet-capture case, doesn't work well for the
request-and-response application case.
I would suggest that:
if the version of libpcap with which you're building has the
pcap_set_immediate_mode() API, use pcap_create(),
pcap_set_immediate_mode(), and pcap_activate() rather than
pcap_open_live(), as libpcap falls back to TPACKET_V2 in immediate mode;
otherwise, libpcap also doesn't support TPACKET_V3, so that's not
an issue - keep using pcap_open_live() (unless you're already using
pcap_create()/pcap_activate(), which first appeared in 1.0.0).
This may require a configure script, if you're OK with building from
source different versions of the program for different machines, or some
dlopen()/dlsym() trickery if you want to make a binary that'll work with
both libpcap 1.5-and-later and earlier versions.
Initial testing on an Ubuntu 14.04 system showed that the pcap_create,
pcap_set_immediate_mode, pcap_activate fixed the problems beautifully for
me. The simplified icmp "server" went from horrible latencies and losses
to a mean round trip time of 298 usec (reported by ping on a 14.04 server
system) and zero losses. Thanks so much for you quick help, and in terms
of the full program, I am very fortunate that it will be compiled and
deployed on a per system basis so I don't need to worry about a generic
binary and can sort out a configure script or Makefile trickery. Thanks
for answering within a few hours a question that has been in the back of
my mind for months.
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