On Thu, Aug 13, 2009 at 4:00 PM, Steve Fink<sph...@gmail.com> wrote: > I have a video stream I am attempting to send over UDP. It should > originally have been playing at 3.75Mbps (payload; about 3.88Mbps or > so wire rate.) When I play it back, tcpreplay reports: > > # tcpreplay -i eth1 /tmp/replay.pcap > sending out eth1 > processing file: /tmp/replay.pcap > Actual: 31823 packets (43215634 bytes) sent in 127.35 seconds > Rated: 339345.4 bps, 2.59 Mbps, 249.89 pps > Statistics for network device: eth1 > Attempted packets: 31823 > Successful packets: 31823 > Failed packets: 0 > Retried packets (ENOBUFS): 0 > Retried packets (EAGAIN): 0
[snip] > This is running inside a Xen VM, so the network device is virtual. I'm > not sure what the physical device is. I can dig that up if needed. The > VM can send at 646 Mbps, though. If I had to guess (and I am guessing) it's that you're running under Xen while using the default gettimeofday() timing mode of tcpreplay. In a perfect world under modern Linux kernels, gettimeofday() does a direct call to the CPU's HPET (high-performance event timer), but with virtualization that won't be possible. Something about how Xen handles the gettimeofday call is most likely causing your problem. You might have better luck using --timer=nano or possibly --timer=select I'd guess calls to the RDTSC is probably also virtualized so that's probably not going to be any better, but it's worth a try I guess (--timer=rdtsc). Honestly, I'm a bit surprised by this... the packet rates you're talking about are so low that even really inaccurate timing methods should work fine- you only need millisecond accuracy. FWIW, you're not the first person using some kind of virtualization to have performance problems. Anyways, I'm still downloading your pcap... if it ever completes I'll take a look and see if I can see anything odd which might explain things, but in general using --pps resolves any issues with broken timestamps (since they are ignored). -- Aaron Turner http://synfin.net/ http://tcpreplay.synfin.net/ - Pcap editing and replay tools for Unix & Windows Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. -- Benjamin Franklin ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Tcpreplay-users mailing list Tcpreplay-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/tcpreplay-users Support Information: http://tcpreplay.synfin.net/trac/wiki/Support
