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Measure actual echo timeout instead of network timeout to first hop

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This commit is contained in:
Keith Winstein
2011-10-13 05:14:19 -04:00
parent 1f23219047
commit 460d4303c2
4 changed files with 50 additions and 14 deletions
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terminaloverlay.cpp
+37 -5
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@@ -92,10 +92,29 @@ void OverlayEngine::apply( Framebuffer &fb ) const
[&fb]( OverlayElement *x ) { x->apply( fb ); } );
}
void OverlayEngine::cull( const Framebuffer &fb )
void PredictionEngine::cull( const Framebuffer &fb )
{
uint64_t now = timestamp();
auto i = elements.begin();
while ( i != elements.end() ) {
/* update echo timeout state */
if ( (*i)->get_validity( fb ) == Correct ) {
double R = now - (*i)->prediction_time;
if ( !RTT_hit ) { /* first measurement */
SRTT = R;
RTTVAR = R / 2;
RTT_hit = true;
} else {
const double alpha = 1.0 / 8.0;
const double beta = 1.0 / 4.0;
RTTVAR = (1 - beta) * RTTVAR + ( beta * fabs( SRTT - R ) );
SRTT = (1 - alpha) * SRTT + ( alpha * R );
}
}
/* eliminate predictions proven correct or incorrect */
if ( (*i)->get_validity( fb ) != Pending ) {
delete (*i);
i = elements.erase( i );
@@ -263,6 +282,8 @@ void NotificationEngine::apply( Framebuffer &fb ) const
void OverlayManager::apply( Framebuffer &fb )
{
predictions.calculate_score( fb );
/* eliminate predictions proven correct or incorrect and update echo timers */
predictions.cull( fb );
if ( predictions.get_score() > 3 ) {
@@ -289,14 +310,14 @@ void PredictionEngine::calculate_score( const Framebuffer &fb )
}
}
void PredictionEngine::new_user_byte( char the_byte, const Framebuffer &fb, int prediction_len )
void PredictionEngine::new_user_byte( char the_byte, const Framebuffer &fb )
{
uint64_t now = timestamp();
if ( elements.empty() ) {
/* starting from scratch */
elements.push_front( new ConditionalCursorMove( now + prediction_len,
elements.push_front( new ConditionalCursorMove( now + prediction_len(),
fb.ds.get_cursor_row(),
fb.ds.get_cursor_col() ) );
}
@@ -313,7 +334,7 @@ void PredictionEngine::new_user_byte( char the_byte, const Framebuffer &fb, int
const Cell *existing_cell = fb.get_cell( ccm->new_row, ccm->new_col );
ConditionalOverlayCell *coc = new ConditionalOverlayCell( now + prediction_len,
ConditionalOverlayCell *coc = new ConditionalOverlayCell( now + prediction_len(),
ccm->new_row, ccm->new_col,
existing_cell->renditions.background_color,
*existing_cell );
@@ -323,7 +344,7 @@ void PredictionEngine::new_user_byte( char the_byte, const Framebuffer &fb, int
coc->replacement.contents.push_back( the_byte );
ccm->new_col++;
ccm->expiration_time = now + prediction_len;
ccm->expiration_time = now + prediction_len();
elements.push_back( coc );
} else {
@@ -357,3 +378,14 @@ int OverlayManager::wait_time( void )
return ret;
}
}
int PredictionEngine::prediction_len( void )
{
uint64_t RTO = lrint( ceil( SRTT + 4 * RTTVAR ) );
if ( RTO < 20 ) {
RTO = 20;
} else if ( RTO > 2000 ) {
RTO = 2000;
}
return RTO;
}