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.
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