david d8ac4f8859 Merge from /nmap-exp/david/nmap-fixed-rate. This brings in ...

doAnyOutstandingProbes performance improvements. Here is the log message from
r7914 in nmap-fixed-rate.

Keep a cache of the most recently processed probe for each host in
doAnyOutstandingRetransmits. This greatly reduces the amount of CPU used by
that function when the lists of outstanding probes grow long, such as when a
high scan rate is specified with --min-rate.

This is not most efficient possible way this could be done, but it is a pretty
big win, and it's very non-invasive. The changes are limited entirely to
doAnyOutstandingRetransmits, with no new global state in ultra_scan.

# nmap -d --min-rate 50000 -n -PN -p1-65535 --max-rtt-timeout 500 --max-retries 1 scanme.nmap.org

gprof before:
  %   cumulative   self              self     total
 time   seconds   seconds    calls   s/call   s/call  name
 49.74     30.96    30.96     2709     0.01     0.02  doAnyOutstandingRetransmits(UltraScanInfo*)
 10.51     37.50     6.54 127256413     0.00     0.00  std::_List_iterator<UltraProbe*>::operator--(int)

gprof after:
  %   cumulative   self              self     total
 time   seconds   seconds    calls   s/call   s/call  name
 20.48      3.36     3.36     2667     0.00     0.00  doAnyOutstandingRetransmits(UltraScanInfo*)
 16.21      6.02     2.66     2667     0.00     0.00  processData(UltraScanInfo*)

Note that 50000 packets per second is way excessive. I really only get about
6000 in practice. But the point is there is no huge CPU penalty for giving an
excessive rate.

2008-06-04 03:45:39 +00:00

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