My version of Time::HiRes doesn't have setitimer, but I get fairly precise results with alarm: 
#!/usr/bin/perl -w

use strict;
use Time::HiRes qw (alarm time);

$SIG{ALRM} = sub { printf "%16.5f\n",time; alarm(0.5); };
alarm(0.5);

while(1)
{
  select(undef,undef,undef,1);
}

[download]
produces 
1069651689.38722
1069651689.88720
1069651690.38720
1069651690.88721
1069651691.38721

If you can't alarms at precise times, you can try to make up for it by printing packets/second, which should be the same even if the alarms are off by a little bit. You may also find that using 1-second intervals works better, since that's the traditional interface provided by alarm, but I'm not sure.

This is on RedHat 7.2, kernel 2.4.20, perl 5.6.1, Time::HiRes 1.20.

In reply to Re: IP Packet count at regular intervals of time by sgifford
in thread IP Packet count at regular intervals of time by prakashrj

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