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Big optimization of doAnyOutstandingRetransmits

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Retransmitting does not change the set of incomplete hosts, so there's
no need to use a map to store the current position in the outstanding
probes queue. Using a vector is much faster. Additionally, improper use
of std::map::find() and std::map::operator[] meant that the O(logN)
lookup was happening 4 times for a single host for each iteration
through the loop. Complexity for N targets is now O(N), not O(N logN)
This commit is contained in:
dmiller
2022-11-02 02:12:39 +00:00
parent a2062c2745
commit ee059c44fe
1 changed files with 25 additions and 14 deletions
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39
scan_engine.cc
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@@ -2437,14 +2437,18 @@ static void retransmitProbe(UltraScanInfo *USI, HostScanStats *hss,
USI->gstats->probes_sent++;
}
struct ProbeCacheNode {
HostScanStats *hss;
std::list<UltraProbe *>::iterator probeI;
};
/* Go through the ProbeQueue of each host, identify any
timed out probes, then try to retransmit them as appropriate */
static void doAnyOutstandingRetransmits(UltraScanInfo *USI) {
std::multiset<HostScanStats *, HssPredicate>::iterator hostI;
std::list<UltraProbe *>::iterator probeI;
/* A cache of the last processed probe from each host, to avoid re-examining a
bunch of probes to find the next one that needs to be retransmitted. */
std::map<HostScanStats *, std::list<UltraProbe *>::iterator> probe_cache;
std::vector<struct ProbeCacheNode> probe_cache;
HostScanStats *host = NULL;
UltraProbe *probe = NULL;
int retrans = 0; /* Number of retransmissions during a loop */
@@ -2457,14 +2461,29 @@ static void doAnyOutstandingRetransmits(UltraScanInfo *USI) {
if (o.debugging)
tv_start = USI->now;
probe_cache.reserve(USI->numIncompleteHosts());
for (hostI = USI->incompleteHosts.begin();
hostI != USI->incompleteHosts.end();
hostI++) {
struct ProbeCacheNode pcn;
pcn.hss = *hostI;
/* Skip this host if it has nothing to send. */
if (pcn.hss->num_probes_active == 0
&& pcn.hss->num_probes_waiting_retransmit == 0)
continue;
assert(!pcn.hss->probes_outstanding.empty());
pcn.probeI = pcn.hss->probes_outstanding.end();
probe_cache.push_back(pcn);
}
/* Loop until we get through all the hosts without a retransmit or we're not
OK to send any more. */
do {
retrans = 0;
for (hostI = USI->incompleteHosts.begin();
hostI != USI->incompleteHosts.end() && USI->gstats->sendOK(NULL);
hostI++) {
host = *hostI;
for (std::vector<struct ProbeCacheNode>::iterator pci = probe_cache.begin();
pci != probe_cache.end() && USI->gstats->sendOK(NULL);
pci++) {
host = pci->hss;
std::list<UltraProbe *>::iterator &probeI = pci->probeI;
/* Skip this host if it has nothing to send. */
if ((host->num_probes_active == 0
&& host->num_probes_waiting_retransmit == 0))
@@ -2473,12 +2492,6 @@ static void doAnyOutstandingRetransmits(UltraScanInfo *USI) {
continue;
assert(!host->probes_outstanding.empty());
/* Initialize the probe cache if necessary. */
if (probe_cache.find(host) == probe_cache.end())
probe_cache[host] = host->probes_outstanding.end();
/* Restore the probe iterator from the cache. */
probeI = probe_cache[host];
maxtries = host->allowedTryno(NULL, NULL);
do {
probeI--;
@@ -2508,8 +2521,6 @@ static void doAnyOutstandingRetransmits(UltraScanInfo *USI) {
/* Wrap the probe iterator around. */
if (probeI == host->probes_outstanding.begin())
probeI = host->probes_outstanding.end();
/* Cache the probe iterator. */
probe_cache[host] = probeI;
}
} while (USI->gstats->sendOK(NULL) && retrans != 0);