From 9e8a59fc9dcabb7a645caf2af22efef9508a84f8 Mon Sep 17 00:00:00 2001
From: Konrad Wojas <github@m.wojas.nl>
Date: Fri, 6 Jul 2018 20:31:13 +0800
Subject: [PATCH] calidns: accurate qps targets

Instead of a naive fixed sleep between batch sends, check the actual time
passed to determine how long to sleep. This allows calidns to actually
reach qps targets at higher rates.
---
 pdns/calidns.cc | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/pdns/calidns.cc b/pdns/calidns.cc
index 64323c484a..a82a4fc03d 100644
--- a/pdns/calidns.cc
+++ b/pdns/calidns.cc
@@ -158,10 +158,14 @@ static void replaceEDNSClientSubnet(vector<uint8_t>* packet, const Netmask& ecsR
 static void sendPackets(const vector<Socket*>* sockets, const vector<vector<uint8_t>* >& packets, int qps, ComboAddress dest, const Netmask& ecsRange)
 {
   unsigned int burst=100;
+  const auto nsecPerBurst=1*(unsigned long)(burst*1000000000.0/qps);
   struct timespec nsec;
   nsec.tv_sec=0;
-  nsec.tv_nsec=1*(unsigned long)(burst*1000000000.0/qps);
+  nsec.tv_nsec=0;
   int count=0;
+  unsigned int nBursts=0;
+  DTime dt;
+  dt.set();
 
   struct Unit {
     struct msghdr msgh;
@@ -187,8 +191,17 @@ static void sendPackets(const vector<Socket*>* sockets, const vector<vector<uint
 	unixDie("sendmmsg");
     
     
-    if(!(count%burst))
-      nanosleep(&nsec, 0);
+    if(!(count%burst)) {
+      nBursts++;
+      // Calculate the time in nsec we need to sleep to the next burst.
+      // If this is negative, it means that we are not achieving the requested
+      // target rate, in which case we skip the sleep.
+      int toSleep = nBursts*nsecPerBurst - 1000*dt.udiffNoReset();
+      if (toSleep > 0) {
+        nsec.tv_nsec = toSleep;
+        nanosleep(&nsec, 0);
+      }
+    }
   }
 }
 
-- 
2.47.2