diff options
| -rw-r--r-- | common/rfb/Congestion.cxx | 357 | ||||
| -rw-r--r-- | common/rfb/Congestion.h | 57 | ||||
| -rw-r--r-- | common/rfb/VNCSConnectionST.cxx | 27 | ||||
| -rw-r--r-- | common/rfb/VNCSConnectionST.h | 1 | ||||
| -rw-r--r-- | common/rfb/util.cxx | 31 | ||||
| -rw-r--r-- | common/rfb/util.h | 8 |
6 files changed, 363 insertions, 118 deletions
diff --git a/common/rfb/Congestion.cxx b/common/rfb/Congestion.cxx index c4c4d96d..94d78e32 100644 --- a/common/rfb/Congestion.cxx +++ b/common/rfb/Congestion.cxx @@ -24,12 +24,16 @@ * The basic principle is TCP Congestion Control (RFC 5618), with the * addition of using the TCP Vegas algorithm. The reason we use Vegas * is that we run on top of a reliable transport so we need a latency - * based algorithm rather than a loss based one. + * based algorithm rather than a loss based one. There is also a lot of + * interpolation of values. This is because we have rather horrible + * granularity in our measurements. */ +#include <assert.h> #include <sys/time.h> #include <rfb/Congestion.h> +#include <rfb/LogWriter.h> #include <rfb/util.h> // Debug output on what the congestion control is up to @@ -49,158 +53,332 @@ static const unsigned MINIMUM_WINDOW = 4096; // limit for now... static const unsigned MAXIMUM_WINDOW = 4194304; -struct Congestion::RTTInfo { - struct timeval tv; - int offset; - unsigned inFlight; -}; +static LogWriter vlog("Congestion"); Congestion::Congestion() : + lastPosition(0), extraBuffer(0), baseRTT(-1), congWindow(INITIAL_WINDOW), - ackedOffset(0), sentOffset(0), - minRTT(-1), seenCongestion(false), - congestionTimer(this) + measurements(0), minRTT(-1), minCongestedRTT(-1) { + gettimeofday(&lastUpdate, NULL); + gettimeofday(&lastSent, NULL); + memset(&lastPong, 0, sizeof(lastPong)); + gettimeofday(&lastPongArrival, NULL); + gettimeofday(&lastAdjustment, NULL); } Congestion::~Congestion() { } +void Congestion::updatePosition(unsigned pos) +{ + struct timeval now; + unsigned delta, consumed; + + gettimeofday(&now, NULL); + + delta = pos - lastPosition; + if ((delta > 0) || (extraBuffer > 0)) + lastSent = now; + + // Idle for too long? + // We use a very crude RTO calculation in order to keep things simple + // FIXME: should implement RFC 2861 + if (msBetween(&lastSent, &now) > __rfbmax(baseRTT*2, 100)) { + +#ifdef CONGESTION_DEBUG + vlog.debug("Connection idle for %d ms, resetting congestion control", + msBetween(&lastSent, &now)); +#endif + + // Close congestion window and redo wire latency measurement + congWindow = __rfbmin(INITIAL_WINDOW, congWindow); + baseRTT = -1; + measurements = 0; + gettimeofday(&lastAdjustment, NULL); + minRTT = minCongestedRTT = -1; + } + + // Commonly we will be in a state of overbuffering. We need to + // estimate the extra delay that causes so we can separate it from + // the delay caused by an incorrect congestion window. + // (we cannot do this until we have a RTT measurement though) + if (baseRTT != (unsigned)-1) { + extraBuffer += delta; + consumed = msBetween(&lastUpdate, &now) * congWindow / baseRTT; + if (extraBuffer < consumed) + extraBuffer = 0; + else + extraBuffer -= consumed; + } + + lastPosition = pos; + lastUpdate = now; +} -void Congestion::sentPing(int offset) +void Congestion::sentPing() { struct RTTInfo rttInfo; - if (ackedOffset == 0) - ackedOffset = offset; - memset(&rttInfo, 0, sizeof(struct RTTInfo)); gettimeofday(&rttInfo.tv, NULL); - rttInfo.offset = offset; - rttInfo.inFlight = rttInfo.offset - ackedOffset; + rttInfo.pos = lastPosition; + rttInfo.extra = getExtraBuffer(); + rttInfo.congested = isCongested(); pings.push_back(rttInfo); - - sentOffset = offset; - - // Let some data flow before we adjust the settings - if (!congestionTimer.isStarted()) - congestionTimer.start(__rfbmin(baseRTT * 2, 100)); } void Congestion::gotPong() { + struct timeval now; struct RTTInfo rttInfo; unsigned rtt, delay; if (pings.empty()) return; + gettimeofday(&now, NULL); + rttInfo = pings.front(); pings.pop_front(); - rtt = msSince(&rttInfo.tv); + lastPong = rttInfo; + lastPongArrival = now; + + rtt = msBetween(&rttInfo.tv, &now); if (rtt < 1) rtt = 1; - ackedOffset = rttInfo.offset; - // Try to estimate wire latency by tracking lowest seen latency if (rtt < baseRTT) baseRTT = rtt; - if (rttInfo.inFlight > congWindow) { - seenCongestion = true; - - // Estimate added delay because of overtaxed buffers - delay = (rttInfo.inFlight - congWindow) * baseRTT / congWindow; + // Pings sent before the last adjustment aren't interesting as they + // aren't a measurement of the current congestion window + if (isBefore(&rttInfo.tv, &lastAdjustment)) + return; - if (delay < rtt) - rtt -= delay; - else - rtt = 1; + // Estimate added delay because of overtaxed buffers (see above) + delay = rttInfo.extra * baseRTT / congWindow; + if (delay < rtt) + rtt -= delay; + else + rtt = 1; - // If we underestimate the congestion window, then we'll get a latency - // that's less than the wire latency, which will confuse other portions - // of the code. - if (rtt < baseRTT) - rtt = baseRTT; - } + // A latency less than the wire latency means that we've + // understimated the congestion window. We can't really determine + // how much, so pretend that we got no buffer latency at all. + if (rtt < baseRTT) + rtt = baseRTT; - // We only keep track of the minimum latency seen (for a given interval) - // on the basis that we want to avoid continuous buffer issue, but don't - // mind (or even approve of) bursts. + // Record the minimum seen delay (hopefully ignores jitter) and let + // the congestion control do its thing. + // + // Note: We are delay based rather than loss based, which means we + // need to look at pongs even if they weren't limited by the + // current window ("congested"). Otherwise we will fail to + // detect increasing congestion until the application exceeds + // the congestion window. if (rtt < minRTT) minRTT = rtt; + if (rttInfo.congested) { + if (rtt < minCongestedRTT) + minCongestedRTT = rtt; + } + + measurements++; + updateCongestion(); } -bool Congestion::isCongested(int offset, unsigned idleTime) +bool Congestion::isCongested() { - // Idle for too long? (and no data on the wire) - // - // FIXME: This should really just be one baseRTT, but we're getting - // problems with triggering the idle timeout on each update. - // Maybe we need to use a moving average for the wire latency - // instead of baseRTT. - if ((sentOffset == ackedOffset) && (idleTime > 2 * baseRTT)) { + if (getInFlight() < congWindow) + return false; -#ifdef CONGESTION_DEBUG - if (congWindow > INITIAL_WINDOW) - fprintf(stderr, "Reverting to initial window (%d KiB) after %d ms\n", - INITIAL_WINDOW / 1024, sock->outStream().getIdleTime()); -#endif + return true; +} - // Close congestion window and allow a transfer - // FIXME: Reset baseRTT like Linux Vegas? - congWindow = __rfbmin(INITIAL_WINDOW, congWindow); +int Congestion::getUncongestedETA() +{ + unsigned targetAcked; + + const struct RTTInfo* prevPing; + unsigned eta, elapsed; + unsigned etaNext, delay; + + std::list<struct RTTInfo>::const_iterator iter; + + targetAcked = lastPosition - congWindow; + + // Simple case? + if (lastPong.pos > targetAcked) + return 0; + + // No measurements yet? + if (baseRTT == (unsigned)-1) + return -1; + + prevPing = &lastPong; + eta = 0; + elapsed = msSince(&lastPongArrival); + + // Walk the ping queue and figure out which one we are waiting for to + // get to an uncongested state + + for (iter = pings.begin(); ;++iter) { + struct RTTInfo curPing; + + // If we aren't waiting for a pong that will clear the congested + // state then we have to estimate the final bit by pretending that + // we had a ping just after the last position update. + if (iter == pings.end()) { + curPing.tv = lastUpdate; + curPing.pos = lastPosition; + curPing.extra = extraBuffer; + } else { + curPing = *iter; + } + + etaNext = msBetween(&prevPing->tv, &curPing.tv); + // Compensate for buffering delays + delay = curPing.extra * baseRTT / congWindow; + etaNext += delay; + delay = prevPing->extra * baseRTT / congWindow; + if (delay >= etaNext) + etaNext = 0; + else + etaNext -= delay; - return false; + // Found it? + if (curPing.pos > targetAcked) { + eta += etaNext * (curPing.pos - targetAcked) / (curPing.pos - prevPing->pos); + if (elapsed > eta) + return 0; + else + return eta - elapsed; + } + + assert(iter != pings.end()); + + eta += etaNext; + prevPing = &*iter; } +} - // FIXME: Should we compensate for non-update data? - // (i.e. use sentOffset instead of offset) - if ((offset - ackedOffset) < congWindow) - return false; +unsigned Congestion::getExtraBuffer() +{ + unsigned elapsed; + unsigned consumed; - // If we just have one outstanding "ping", that means the client has - // started receiving our update. In order to not regress compared to - // before we had congestion avoidance, we allow another update here. - // This could further clog up the tubes, but congestion control isn't - // really working properly right now anyway as the wire would otherwise - // be idle for at least RTT/2. - if (pings.size() == 1) - return false; + if (baseRTT == (unsigned)-1) + return 0; - return true; + elapsed = msSince(&lastUpdate); + consumed = elapsed * congWindow / baseRTT; + + if (consumed >= extraBuffer) + return 0; + else + return extraBuffer - consumed; } -bool Congestion::handleTimeout(Timer* t) +unsigned Congestion::getInFlight() +{ + struct RTTInfo nextPong; + unsigned etaNext, delay, elapsed, acked; + + // Simple case? + if (lastPosition == lastPong.pos) + return 0; + + // No measurements yet? + if (baseRTT == (unsigned)-1) { + if (!pings.empty()) + return lastPosition - pings.front().pos; + return 0; + } + + // If we aren't waiting for any pong then we have to estimate things + // by pretending that we had a ping just after the last position + // update. + if (pings.empty()) { + nextPong.tv = lastUpdate; + nextPong.pos = lastPosition; + nextPong.extra = extraBuffer; + } else { + nextPong = pings.front(); + } + + // First we need to estimate how many bytes have made it through + // completely. Look at the next ping that should arrive and figure + // out how far behind it should be and interpolate the positions. + + etaNext = msBetween(&lastPong.tv, &nextPong.tv); + // Compensate for buffering delays + delay = nextPong.extra * baseRTT / congWindow; + etaNext += delay; + delay = lastPong.extra * baseRTT / congWindow; + if (delay >= etaNext) + etaNext = 0; + else + etaNext -= delay; + + elapsed = msSince(&lastPongArrival); + + // The pong should be here any second. Be optimistic and assume + // we can already use its value. + if (etaNext <= elapsed) + acked = nextPong.pos; + else { + acked = lastPong.pos; + acked += (nextPong.pos - lastPong.pos) * elapsed / etaNext; + } + + return lastPosition - acked; +} + +void Congestion::updateCongestion() { unsigned diff; - if (!seenCongestion) - return false; + // We want at least three measurements to avoid noise + if (measurements < 3) + return; + + assert(minRTT >= baseRTT); + assert(minCongestedRTT >= baseRTT); // The goal is to have a slightly too large congestion window since // a "perfect" one cannot be distinguished from a too small one. This // translates to a goal of a few extra milliseconds of delay. + // First we check all pongs to make sure we're not having a too large + // congestion window. diff = minRTT - baseRTT; - if (diff > __rfbmin(100, baseRTT)) { + // FIXME: Should we do slow start? + if (diff > 100) { // Way too fast congWindow = congWindow * baseRTT / minRTT; - } else if (diff > __rfbmin(50, baseRTT/2)) { + } else if (diff > 50) { // Slightly too fast congWindow -= 4096; - } else if (diff < 5) { - // Way too slow - congWindow += 8192; - } else if (diff < 25) { - // Too slow - congWindow += 4096; + } else { + // Secondly only the "congested" pongs are checked to see if the + // window is too small. + + diff = minCongestedRTT - baseRTT; + + if (diff < 5) { + // Way too slow + congWindow += 8192; + } else if (diff < 25) { + // Too slow + congWindow += 4096; + } } if (congWindow < MINIMUM_WINDOW) @@ -209,14 +387,13 @@ bool Congestion::handleTimeout(Timer* t) congWindow = MAXIMUM_WINDOW; #ifdef CONGESTION_DEBUG - fprintf(stderr, "RTT: %d ms (%d ms), Window: %d KiB, Bandwidth: %g Mbps\n", - minRTT, baseRTT, congWindow / 1024, - congWindow * 8.0 / baseRTT / 1000.0); + vlog.debug("RTT: %d ms (%d ms), Window: %d KiB, Bandwidth: %g Mbps", + minRTT, baseRTT, congWindow / 1024, + congWindow * 8.0 / baseRTT / 1000.0); #endif - minRTT = -1; - seenCongestion = false; - - return false; + measurements = 0; + gettimeofday(&lastAdjustment, NULL); + minRTT = minCongestedRTT = -1; } diff --git a/common/rfb/Congestion.h b/common/rfb/Congestion.h index e8548f93..2bea5dac 100644 --- a/common/rfb/Congestion.h +++ b/common/rfb/Congestion.h @@ -21,41 +21,62 @@ #include <list> -#include <rfb/Timer.h> - namespace rfb { - class Congestion : public Timer::Callback { + class Congestion { public: Congestion(); ~Congestion(); + // updatePosition() registers the current stream position and can + // and should be called often. + void updatePosition(unsigned pos); + // sentPing() must be called when a marker is placed on the - // outgoing stream, along with the current stream position. - // gotPong() must be called when the response for such a marker - // is received. - void sentPing(int offset); + // outgoing stream. gotPong() must be called when the response for + // such a marker is received. + void sentPing(); void gotPong(); // isCongested() determines if the transport is currently congested - // or if more data can be sent. The curren stream position and how - // long the transport has been idle must be specified. - bool isCongested(int offset, unsigned idleTime); + // or if more data can be sent. + bool isCongested(); - private: - // Timer callbacks - virtual bool handleTimeout(Timer* t); + // getUncongestedETA() returns the number of milliseconds until the + // transport is no longer congested. Returns 0 if there is no + // congestion, and -1 if it is unknown when the transport will no + // longer be congested. + int getUncongestedETA(); + + protected: + unsigned getExtraBuffer(); + unsigned getInFlight(); + + void updateCongestion(); private: + unsigned lastPosition; + unsigned extraBuffer; + struct timeval lastUpdate; + struct timeval lastSent; + unsigned baseRTT; unsigned congWindow; - unsigned ackedOffset, sentOffset; - unsigned minRTT; - bool seenCongestion; - Timer congestionTimer; + struct RTTInfo { + struct timeval tv; + unsigned pos; + unsigned extra; + bool congested; + }; - struct RTTInfo; std::list<struct RTTInfo> pings; + + struct RTTInfo lastPong; + struct timeval lastPongArrival; + + int measurements; + struct timeval lastAdjustment; + unsigned minRTT, minCongestedRTT; }; } diff --git a/common/rfb/VNCSConnectionST.cxx b/common/rfb/VNCSConnectionST.cxx index 43eb8256..b2ceb7d2 100644 --- a/common/rfb/VNCSConnectionST.cxx +++ b/common/rfb/VNCSConnectionST.cxx @@ -43,7 +43,7 @@ VNCSConnectionST::VNCSConnectionST(VNCServerST* server_, network::Socket *s, : sock(s), reverseConnection(reverse), queryConnectTimer(this), inProcessMessages(false), pendingSyncFence(false), syncFence(false), fenceFlags(0), - fenceDataLen(0), fenceData(NULL), + fenceDataLen(0), fenceData(NULL), congestionTimer(this), server(server_), updates(false), updateRenderedCursor(false), removeRenderedCursor(false), continuousUpdates(false), encodeManager(this), pointerEventTime(0), @@ -726,6 +726,8 @@ bool VNCSConnectionST::handleTimeout(Timer* t) if (t == &queryConnectTimer) { if (state() == RFBSTATE_QUERYING) approveConnection(false, "The attempt to prompt the user to accept the connection failed"); + } else if (t == &congestionTimer) { + writeFramebufferUpdate(); } } catch (rdr::Exception& e) { close(e.str()); @@ -742,6 +744,8 @@ void VNCSConnectionST::writeRTTPing() if (!cp.supportsFence) return; + congestion.updatePosition(sock->outStream().length()); + // We need to make sure any old update are already processed by the // time we get the response back. This allows us to reliably throttle // back on client overload, as well as network overload. @@ -749,11 +753,15 @@ void VNCSConnectionST::writeRTTPing() writer()->writeFence(fenceFlagRequest | fenceFlagBlockBefore, sizeof(type), &type); - congestion.sentPing(sock->outStream().length()); + congestion.sentPing(); } bool VNCSConnectionST::isCongested() { + unsigned eta; + + congestionTimer.stop(); + // Stuff still waiting in the send buffer? sock->outStream().flush(); if (sock->outStream().bufferUsage() > 0) @@ -762,13 +770,22 @@ bool VNCSConnectionST::isCongested() if (!cp.supportsFence) return false; - return congestion.isCongested(sock->outStream().length(), - sock->outStream().getIdleTime()); + congestion.updatePosition(sock->outStream().length()); + if (!congestion.isCongested()) + return false; + + eta = congestion.getUncongestedETA(); + if (eta >= 0) + congestionTimer.start(eta); + + return true; } void VNCSConnectionST::writeFramebufferUpdate() { + congestion.updatePosition(sock->outStream().length()); + // We're in the middle of processing a command that's supposed to be // synchronised. Allowing an update to slip out right now might violate // that synchronisation. @@ -805,6 +822,8 @@ void VNCSConnectionST::writeFramebufferUpdate() writeDataUpdate(); network::TcpSocket::cork(sock->getFd(), false); + + congestion.updatePosition(sock->outStream().length()); } void VNCSConnectionST::writeNoDataUpdate() diff --git a/common/rfb/VNCSConnectionST.h b/common/rfb/VNCSConnectionST.h index 96d7e4c9..dde0b1ec 100644 --- a/common/rfb/VNCSConnectionST.h +++ b/common/rfb/VNCSConnectionST.h @@ -187,6 +187,7 @@ namespace rfb { char *fenceData; Congestion congestion; + Timer congestionTimer; VNCServerST* server; SimpleUpdateTracker updates; diff --git a/common/rfb/util.cxx b/common/rfb/util.cxx index 22e00ffc..755c91fd 100644 --- a/common/rfb/util.cxx +++ b/common/rfb/util.cxx @@ -121,19 +121,38 @@ namespace rfb { dest[src ? destlen-1 : 0] = 0; } + unsigned msBetween(const struct timeval *first, + const struct timeval *second) + { + unsigned diff; + + diff = (second->tv_sec - first->tv_sec) * 1000; + + diff += second->tv_usec / 1000; + diff -= first->tv_usec / 1000; + + return diff; + } + unsigned msSince(const struct timeval *then) { struct timeval now; - unsigned diff; gettimeofday(&now, NULL); - diff = (now.tv_sec - then->tv_sec) * 1000; - - diff += now.tv_usec / 1000; - diff -= then->tv_usec / 1000; + return msBetween(then, &now); + } - return diff; + bool isBefore(const struct timeval *first, + const struct timeval *second) + { + if (first->tv_sec < second->tv_sec) + return true; + if (first->tv_sec > second->tv_sec) + return false; + if (first->tv_usec < second->tv_usec) + return true; + return false; } static size_t doPrefix(long long value, const char *unit, diff --git a/common/rfb/util.h b/common/rfb/util.h index e9114c3d..3ca92f9d 100644 --- a/common/rfb/util.h +++ b/common/rfb/util.h @@ -95,9 +95,17 @@ namespace rfb { return (secs < 0 || secs > (INT_MAX/1000) ? INT_MAX : secs * 1000); } + // Returns time elapsed between two moments in milliseconds. + unsigned msBetween(const struct timeval *first, + const struct timeval *second); + // Returns time elapsed since given moment in milliseconds. unsigned msSince(const struct timeval *then); + // Returns true if first happened before seconds + bool isBefore(const struct timeval *first, + const struct timeval *second); + size_t siPrefix(long long value, const char *unit, char *buffer, size_t maxlen, int precision=6); size_t iecPrefix(long long value, const char *unit, |