From d718f1b9fd8893a77b18e89cf6cce5ac7fbc3a7b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E4=B8=96=E7=95=8C?= <i@sekai.icu>
Date: Sun, 28 Apr 2024 12:41:34 +0800
Subject: [PATCH] hysteria: Improve pacer

---
 hysteria/congestion/pacer.go | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/hysteria/congestion/pacer.go b/hysteria/congestion/pacer.go
index a648f98..3b0a04f 100644
--- a/hysteria/congestion/pacer.go
+++ b/hysteria/congestion/pacer.go
@@ -1,15 +1,15 @@
 package congestion
 
 import (
-	"math"
 	"time"
 
 	"github.com/sagernet/quic-go/congestion"
 )
 
 const (
-	maxBurstPackets = 10
-	minPacingDelay  = time.Millisecond
+	maxBurstPackets               = 10
+	maxBurstPacingDelayMultiplier = 4
+	minPacingDelay                = time.Millisecond
 )
 
 // The pacer implements a token bucket pacing algorithm.
@@ -52,7 +52,7 @@ func (p *pacer) Budget(now time.Time) congestion.ByteCount {
 
 func (p *pacer) maxBurstSize() congestion.ByteCount {
 	return maxByteCount(
-		congestion.ByteCount((minPacingDelay+time.Millisecond).Nanoseconds())*p.getBandwidth()/1e9,
+		congestion.ByteCount((maxBurstPacingDelayMultiplier*minPacingDelay).Nanoseconds())*p.getBandwidth()/1e9,
 		maxBurstPackets*p.maxDatagramSize,
 	)
 }
@@ -63,11 +63,16 @@ func (p *pacer) TimeUntilSend() time.Time {
 	if p.budgetAtLastSent >= p.maxDatagramSize {
 		return time.Time{}
 	}
-	return p.lastSentTime.Add(maxDuration(
-		minPacingDelay,
-		time.Duration(math.Ceil(float64(p.maxDatagramSize-p.budgetAtLastSent)*1e9/
-			float64(p.getBandwidth())))*time.Nanosecond,
-	))
+	diff := 1e9 * uint64(p.maxDatagramSize-p.budgetAtLastSent)
+	bw := uint64(p.getBandwidth())
+	// We might need to round up this value.
+	// Otherwise, we might have a budget (slightly) smaller than the datagram size when the timer expires.
+	d := diff / bw
+	// this is effectively a math.Ceil, but using only integer math
+	if diff%bw > 0 {
+		d++
+	}
+	return p.lastSentTime.Add(maxDuration(congestion.MinPacingDelay, time.Duration(d)*time.Nanosecond))
 }
 
 func (p *pacer) SetMaxDatagramSize(s congestion.ByteCount) {