bug 729736 - runtime experiment with different spdy ping thresholds r=honzab

modules/libpref/src/init/all.js

@@ -678,6 +678,11 @@ pref("security.fileuri.strict_origin_policy", true);
 // prevents necko connecting to ports 1-5 unless the protocol
 // overrides.
 
+// Allow necko to do A/B testing. Will generally only happen if
+// telemetry is also enabled as otherwise there is no way to report
+// the results
+pref("network.allow-experiments", true);
+
 // Default action for unlisted external protocol handlers
 pref("network.protocol-handler.external-default", true);      // OK to load
 pref("network.protocol-handler.warn-external-default", true); // warn before load

netwerk/base/src/nsSocketTransportService2.cpp

@@ -632,6 +632,9 @@ nsSocketTransportService::Run()
     nsCOMPtr<nsIThreadInternal> threadInt = do_QueryInterface(thread);
     threadInt->SetObserver(this);
 
+    // make sure the pseudo random number generator is seeded on this thread
+    srand(PR_Now());
+
     for (;;) {
         bool pendingEvents = false;
         thread->HasPendingEvents(&pendingEvents);

netwerk/protocol/http/SpdySession.cpp

@@ -93,7 +93,8 @@ SpdySession::SpdySession(nsAHttpTransaction *aHttpTransaction,
     mOutputQueueSent(0),
     mLastReadEpoch(PR_IntervalNow()),
     mPingSentEpoch(0),
-    mNextPingID(1)
+    mNextPingID(1),
+    mPingThresholdExperiment(false)
 {
   NS_ABORT_IF_FALSE(PR_GetCurrentThread() == gSocketThread, "wrong thread");
 
@@ -111,6 +112,41 @@ SpdySession::SpdySession(nsAHttpTransaction *aHttpTransaction,
   mSendingChunkSize = gHttpHandler->SpdySendingChunkSize();
   AddStream(aHttpTransaction, firstPriority);
   mLastDataReadEpoch = mLastReadEpoch;
+  
+  DeterminePingThreshold();
+}
+
+void
+SpdySession::DeterminePingThreshold()
+{
+  mPingThreshold = gHttpHandler->SpdyPingThreshold();
+
+  if (!mPingThreshold || !gHttpHandler->AllowExperiments())
+    return;
+
+  PRUint32 randomVal = gHttpHandler->Get32BitsOfPseudoRandom();
+  
+  // Use the lower 10 bits to select 1 in 1024 sessions for the
+  // ping threshold experiment. Somewhat less than that will actually be
+  // used because random values greater than the total http idle timeout
+  // for the session are discarded.
+  if ((randomVal & 0x3ff) != 1)  // lottery
+    return;
+  
+  randomVal = randomVal >> 10; // those bits are used up
+
+  // This session has been selected - use a random ping threshold of 10 +
+  // a random number from 0 to 255, based on the next 8 bits of the
+  // random buffer
+  PRIntervalTime randomThreshold =
+    PR_SecondsToInterval((randomVal & 0xff) + 10);
+  if (randomThreshold > gHttpHandler->IdleTimeout())
+    return;
+  
+  mPingThreshold = randomThreshold;
+  mPingThresholdExperiment = true;
+  LOG3(("SpdySession %p Ping Threshold Experimental Selection : %dsec\n",
+        this, PR_IntervalToSeconds(mPingThreshold)));
 }
 
 PLDHashOperator
@@ -228,16 +264,16 @@ SpdySession::ReadTimeoutTick(PRIntervalTime now)
     NS_ABORT_IF_FALSE(PR_GetCurrentThread() == gSocketThread, "wrong thread");
     NS_ABORT_IF_FALSE(mNextPingID & 1, "Ping Counter Not Odd");
 
-    PRIntervalTime threshold = gHttpHandler->SpdyPingThreshold();
+    if (!mPingThreshold)
-    if (!threshold)
       return;
 
     LOG(("SpdySession::ReadTimeoutTick %p delta since last read %ds\n",
          this, PR_IntervalToSeconds(now - mLastReadEpoch)));
 
-    if ((now - mLastReadEpoch) < threshold) {
+    if ((now - mLastReadEpoch) < mPingThreshold) {
       // recent activity means ping is not an issue
-      mPingSentEpoch = 0;
+      if (mPingSentEpoch)
+        ClearPing(true);
       return;
     }
 
@@ -246,6 +282,7 @@ SpdySession::ReadTimeoutTick(PRIntervalTime now)
       if ((now - mPingSentEpoch) >= gHttpHandler->SpdyPingTimeout()) {
         LOG(("SpdySession::ReadTimeoutTick %p Ping Timer Exhaustion\n",
              this));
+        ClearPing(false);
         Close(NS_ERROR_NET_TIMEOUT);
       }
       return;
@@ -273,6 +310,27 @@ SpdySession::ReadTimeoutTick(PRIntervalTime now)
     }
 }
 
+void
+SpdySession::ClearPing(bool pingOK)
+{
+  mPingSentEpoch = 0;
+
+  if (mPingThresholdExperiment) {
+    LOG3(("SpdySession::ClearPing %p mPingThresholdExperiment %dsec %s\n",
+          this, PR_IntervalToSeconds(mPingThreshold),
+          pingOK ? "pass" :"fail"));
+
+    if (pingOK)
+      Telemetry::Accumulate(Telemetry::SPDY_PING_EXPERIMENT_PASS,
+                            PR_IntervalToSeconds(mPingThreshold));
+    else
+      Telemetry::Accumulate(Telemetry::SPDY_PING_EXPERIMENT_FAIL,
+                            PR_IntervalToSeconds(mPingThreshold));
+    mPingThreshold = gHttpHandler->SpdyPingThreshold();
+    mPingThresholdExperiment = false;
+  }
+}
+
 PRUint32
 SpdySession::RegisterStreamID(SpdyStream *stream)
 {
@@ -1187,7 +1245,7 @@ SpdySession::HandlePing(SpdySession *self)
 
   if (pingID & 0x01) {
     // presumably a reply to our timeout ping
-    self->mPingSentEpoch = 0;
+    self->ClearPing(true);
   }
   else {
     // Servers initiate even numbered pings, go ahead and echo it back

netwerk/protocol/http/SpdySession.h

@@ -188,6 +188,7 @@ private:
     PROCESSING_CONTROL_RST_STREAM
   };
 
+  void        DeterminePingThreshold();
   nsresult    HandleSynReplyForValidStream();
   PRUint32    GetWriteQueueSize();
   void        ChangeDownstreamState(enum stateType);
@@ -198,6 +199,7 @@ private:
   nsresult    ConvertHeaders(nsDependentCSubstring &,
                              nsDependentCSubstring &);
   void        GeneratePing(PRUint32);
+  void        ClearPing(bool);
   void        GenerateRstStream(PRUint32, PRUint32);
   void        GenerateGoAway();
   void        CleanupStream(SpdyStream *, nsresult, rstReason);
@@ -345,10 +347,12 @@ private:
   PRUint32             mOutputQueueSent;
   nsAutoArrayPtr<char> mOutputQueueBuffer;
 
+  PRIntervalTime       mPingThreshold;
   PRIntervalTime       mLastReadEpoch;     // used for ping timeouts
   PRIntervalTime       mLastDataReadEpoch; // used for IdleTime()
   PRIntervalTime       mPingSentEpoch;
   PRUint32             mNextPingID;
+  bool                 mPingThresholdExperiment;
 };
 
 }} // namespace mozilla::net

netwerk/protocol/http/nsHttpHandler.cpp

@@ -128,6 +128,8 @@ static NS_DEFINE_CID(kSocketProviderServiceCID, NS_SOCKETPROVIDERSERVICE_CID);
 #define NETWORK_ENABLEIDN       "network.enableIDN"
 #define BROWSER_PREF_PREFIX     "browser.cache."
 #define DONOTTRACK_HEADER_ENABLED "privacy.donottrackheader.enabled"
+#define TELEMETRY_ENABLED        "toolkit.telemetry.enabled"
+#define ALLOW_EXPERIMENTS        "network.allow-experiments"
 
 #define UA_PREF(_pref) UA_PREF_PREFIX _pref
 #define HTTP_PREF(_pref) HTTP_PREF_PREFIX _pref
@@ -200,6 +202,8 @@ nsHttpHandler::nsHttpHandler()
     , mSendSecureXSiteReferrer(true)
     , mEnablePersistentHttpsCaching(false)
     , mDoNotTrackEnabled(false)
+    , mTelemetryEnabled(false)
+    , mAllowExperiments(true)
     , mEnableSpdy(false)
     , mCoalesceSpdy(true)
     , mUseAlternateProtocol(false)
@@ -268,6 +272,7 @@ nsHttpHandler::Init()
         prefBranch->AddObserver(NETWORK_ENABLEIDN, this, true);
         prefBranch->AddObserver(BROWSER_PREF("disk_cache_ssl"), this, true);
         prefBranch->AddObserver(DONOTTRACK_HEADER_ENABLED, this, true);
+        prefBranch->AddObserver(TELEMETRY_ENABLED, this, true);
 
         PrefsChanged(prefBranch, nsnull);
     }
@@ -536,6 +541,27 @@ nsHttpHandler::GetIOService(nsIIOService** result)
     return NS_OK;
 }
 
+PRUint32
+nsHttpHandler::Get32BitsOfPseudoRandom()
+{
+    // only confirm rand seeding on socket thread
+    NS_ABORT_IF_FALSE(PR_GetCurrentThread() == gSocketThread, "wrong thread");
+
+    // rand() provides different amounts of PRNG on different platforms.
+    // 15 or 31 bits are common amounts.
+
+    PR_STATIC_ASSERT(RAND_MAX >= 0xfff);
+    
+#if RAND_MAX < 0xffffU
+    return ((PRUint16) rand() << 20) |
+            (((PRUint16) rand() & 0xfff) << 8) |
+            ((PRUint16) rand() & 0xff);
+#elif RAND_MAX < 0xffffffffU
+    return ((PRUint16) rand() << 16) | ((PRUint16) rand() & 0xffff);
+#else
+    return (PRUint32) rand();
+#endif
+}
 
 void
 nsHttpHandler::NotifyObservers(nsIHttpChannel *chan, const char *event)
@@ -1187,6 +1213,30 @@ nsHttpHandler::PrefsChanged(nsIPrefBranch *prefs, const char *pref)
         }
     }
 
+    //
+    // Telemetry
+    //
+
+    if (PREF_CHANGED(TELEMETRY_ENABLED)) {
+        cVar = false;
+        rv = prefs->GetBoolPref(TELEMETRY_ENABLED, &cVar);
+        if (NS_SUCCEEDED(rv)) {
+            mTelemetryEnabled = cVar;
+        }
+    }
+
+    //
+    // network.allow-experiments
+    //
+
+    if (PREF_CHANGED(ALLOW_EXPERIMENTS)) {
+        cVar = true;
+        rv = prefs->GetBoolPref(ALLOW_EXPERIMENTS, &cVar);
+        if (NS_SUCCEEDED(rv)) {
+            mAllowExperiments = cVar;
+        }
+    }
+
 #undef PREF_CHANGED
 #undef MULTI_PREF_CHANGED
 }

netwerk/protocol/http/nsHttpHandler.h

@@ -112,6 +112,8 @@ public:
     PRUint32       MaxSocketCount();
 
     bool           IsPersistentHttpsCachingEnabled() { return mEnablePersistentHttpsCaching; }
+    bool           IsTelemetryEnabled() { return mTelemetryEnabled; }
+    bool           AllowExperiments() { return mTelemetryEnabled && mAllowExperiments; }
 
     bool           IsSpdyEnabled() { return mEnableSpdy; }
     bool           CoalesceSpdy() { return mCoalesceSpdy; }
@@ -191,6 +193,9 @@ public:
     nsICookieService * GetCookieService(); // not addrefed
     nsIStrictTransportSecurityService * GetSTSService();
 
+    // callable from socket thread only
+    PRUint32 Get32BitsOfPseudoRandom();
+
     // Called by the channel before writing a request
     void OnModifyRequest(nsIHttpChannel *chan)
     {
@@ -343,6 +348,12 @@ private:
     // For broadcasting the preference to not be tracked
     bool           mDoNotTrackEnabled;
     
+    // Whether telemetry is reported or not
+    bool           mTelemetryEnabled;
+
+    // The value of network.allow-experiments
+    bool           mAllowExperiments;
+
     // Try to use SPDY features instead of HTTP/1.1 over SSL
     bool           mEnableSpdy;
     bool           mCoalesceSpdy;

toolkit/components/telemetry/TelemetryHistograms.h

@@ -200,6 +200,8 @@ HISTOGRAM(SPDY_SYN_REPLY_RATIO, 1, 99, 20, LINEAR,  "SPDY: SYN Reply Header Rati
 HISTOGRAM(SPDY_NPN_CONNECT, 0, 1, 2, BOOLEAN,  "SPDY: NPN Negotiated")
 HISTOGRAM(SPDY_NPN_JOIN, 0, 1, 2, BOOLEAN,  "SPDY: Coalesce Succeeded")
 HISTOGRAM(SPDY_KBREAD_PER_CONN, 1, 3000, 50, EXPONENTIAL, "SPDY: KB read per connection")
+HISTOGRAM(SPDY_PING_EXPERIMENT_PASS, 10, 355, 64, LINEAR, "SPDY: Ping Interval Passed")
+HISTOGRAM(SPDY_PING_EXPERIMENT_FAIL, 10, 355, 64, LINEAR, "SPDY: Ping Interval Failed")
 
 HISTOGRAM(SPDY_SETTINGS_UL_BW, 1, 10000, 100, EXPONENTIAL,  "SPDY: Settings Upload Bandwidth")
 HISTOGRAM(SPDY_SETTINGS_DL_BW, 1, 10000, 100, EXPONENTIAL,  "SPDY: Settings Download Bandwidth")