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// --------------------------------------------------------------------------
//
// File
// Name: TcpNice.cpp
// Purpose: Calculator for adaptive TCP window sizing to support
// low-priority background flows using the stochastic
// algorithm, as described in
// http://www.thlab.net/~lmassoul/p18-key.pdf
// Created: 11/02/2012
//
// --------------------------------------------------------------------------
#include "Box.h"
#include "TcpNice.h"
#include "Logging.h"
#include "BoxTime.h"
#ifdef HAVE_NETINET_TCP_H
# include <netinet/tcp.h>
#endif
#ifdef HAVE_WINSOCK2_H
# include <winsock2.h>
#endif
#ifdef HAVE_SYS_SOCKET_H
# include <sys/socket.h>
#endif
#include "MemLeakFindOn.h"
// --------------------------------------------------------------------------
//
// Function
// Name: TcpNice::TcpNice()
// Purpose: Initialise state of the calculator
// Created: 11/02/2012
//
// --------------------------------------------------------------------------
TcpNice::TcpNice()
: mLastWindowSize(1),
mGammaPercent(100),
mAlphaStar(100),
mDeltaPercent(10)
{
mRateEstimateMovingAverage[0] = 0;
mRateEstimateMovingAverage[1] = 0;
}
// --------------------------------------------------------------------------
//
// Function
// Name: int GetNextWindowSize(int bytesChange,
// box_time_t timeElapsed, int rttEstimateMillis)
// Purpose: Calculate the next recommended window size, given the
// number of bytes sent since the previous recommendation,
// and the time elapsed.
// Created: 11/02/2012
//
// --------------------------------------------------------------------------
int TcpNice::GetNextWindowSize(int bytesChange, box_time_t timeElapsed,
int rttEstimateMicros)
{
int epsilon = (mAlphaStar * 1000000) / rttEstimateMicros;
// timeElapsed is in microseconds, so this will fail for T > 2000 seconds
int rateLastPeriod = ((uint64_t)bytesChange * 1000000 / timeElapsed);
int rawAdjustment = epsilon + rateLastPeriod -
mRateEstimateMovingAverage[0];
int gammaAdjustment = (rawAdjustment * mGammaPercent) / 100;
int newWindowSize = mLastWindowSize + gammaAdjustment;
int newRateEstimateMovingAverage =
(((100 - mDeltaPercent) * mRateEstimateMovingAverage[1]) / 100) +
((mDeltaPercent * rateLastPeriod) / 100);
/*
* b is the number of bytes sent during the previous control period
* T is the length (in us) of the previous control period
* rtt is the round trip time (in us) reported by the kernel on the socket
* e is epsilon, a parameter of the formula, calculated as alpha/rtt
* rb is the actual rate (goodput) over the previous period
* rbhat is the previous (last-but-one) EWMA rate estimate
* raw is the unscaled adjustment to the window size
* gamma is the scaled adjustment to the window size
* wb is the final window size
*/
BOX_TRACE("TcpNice: "
"b=" << bytesChange << ", "
"T=" << timeElapsed << ", "
"rtt=" << rttEstimateMicros << ", "
"e=" << epsilon << ", "
"rb=" << rateLastPeriod << ", "
"rbhat=" << newRateEstimateMovingAverage << ", "
"raw=" << rawAdjustment << ", "
"gamma=" << gammaAdjustment << ", "
"wb=" << newWindowSize);
mRateEstimateMovingAverage[0] = mRateEstimateMovingAverage[1];
mRateEstimateMovingAverage[1] = newRateEstimateMovingAverage;
mLastWindowSize = newWindowSize;
return newWindowSize;
}
// --------------------------------------------------------------------------
//
// Constructor
// Name: NiceSocketStream::NiceSocketStream(
// std::auto_ptr<SocketStream> apSocket)
// Purpose: Initialise state of the socket wrapper
// Created: 11/02/2012
//
// --------------------------------------------------------------------------
NiceSocketStream::NiceSocketStream(std::auto_ptr<SocketStream> apSocket)
: mapSocket(apSocket),
mTcpNice(),
mBytesWrittenThisPeriod(0),
mPeriodStartTime(GetCurrentBoxTime()),
mTimeIntervalMillis(1000),
mEnabled(false)
{ }
// --------------------------------------------------------------------------
//
// Function
// Name: NiceSocketStream::Write(const void *pBuffer, int NBytes)
// Purpose: Writes bytes to the underlying stream, adjusting window size
// using a TcpNice calculator.
// Created: 2012/02/11
//
// --------------------------------------------------------------------------
void NiceSocketStream::Write(const void *pBuffer, int NBytes)
{
#if HAVE_DECL_SO_SNDBUF && HAVE_DECL_TCP_INFO
if(mEnabled && mapTimer.get() && mapTimer->HasExpired())
{
box_time_t newPeriodStart = GetCurrentBoxTime();
box_time_t elapsed = newPeriodStart - mPeriodStartTime;
int socket = mapSocket->GetSocketHandle();
int rtt = 50; // WAG
# if HAVE_DECL_SOL_TCP && defined HAVE_STRUCT_TCP_INFO_TCPI_RTT
struct tcp_info info;
socklen_t optlen = sizeof(info);
if(getsockopt(socket, SOL_TCP, TCP_INFO, &info, &optlen) == -1)
{
BOX_LOG_SYS_WARNING("getsockopt(" << socket << ", SOL_TCP, "
"TCP_INFO) failed");
}
else if(optlen < sizeof(info))
{
BOX_WARNING("getsockopt(" << socket << ", SOL_TCP, "
"TCP_INFO) return structure size " << optlen << ", "
"expected " << sizeof(info));
}
else
{
rtt = info.tcpi_rtt;
}
# endif // HAVE_DECL_SOL_TCP && defined HAVE_STRUCT_TCP_INFO_TCPI_RTT
int newWindow = mTcpNice.GetNextWindowSize(mBytesWrittenThisPeriod,
elapsed, rtt);
if(setsockopt(socket, SOL_SOCKET, SO_SNDBUF, &newWindow,
sizeof(newWindow)) == -1)
{
BOX_LOG_SYS_WARNING("getsockopt(" << socket << ", SOL_SOCKET, "
"SO_SNDBUF, " << newWindow << ") failed");
}
StopTimer();
}
if(mEnabled && !mapTimer.get())
{
// Don't start the timer until we receive the first data to write,
// as diffing might take a long time and we don't want to bias
// the TcpNice algorithm by running while we don't have bulk data
// to send.
StartTimer();
mPeriodStartTime = GetCurrentBoxTime();
mBytesWrittenThisPeriod = 0;
}
mBytesWrittenThisPeriod += NBytes;
#endif // HAVE_DECL_SO_SNDBUF
mapSocket->Write(pBuffer, NBytes);
}
// --------------------------------------------------------------------------
//
// Function
// Name: NiceSocketStream::SetEnabled(bool enabled)
// Purpose: Update the enabled status, and if disabling, cancel the
// timer and set a sensible window size.
// Created: 2012/02/12
//
// --------------------------------------------------------------------------
void NiceSocketStream::SetEnabled(bool enabled)
{
mEnabled = enabled;
if(!enabled)
{
StopTimer();
#if HAVE_DECL_SO_SNDBUF
int socket = mapSocket->GetSocketHandle();
int newWindow = 1<<17;
if(setsockopt(socket, SOL_SOCKET, SO_SNDBUF,
# ifdef WIN32
// optval is a const char * on Windows, even
// though the argument is a boolean or integer,
// for reasons best known to Microsoft!
(const char *)&newWindow,
# else
&newWindow,
# endif
sizeof(newWindow)) == -1)
{
BOX_LOG_SYS_WARNING("getsockopt(" << socket << ", SOL_SOCKET, "
"SO_SNDBUF, " << newWindow << ") failed");
}
#endif
}
}
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