From 0686d815ab3aa5cfceb08ca9b2b16e8b7756ba1b Mon Sep 17 00:00:00 2001
From: xh4n3 <xyn1016@gmail.com>
Date: Tue, 5 Sep 2023 18:46:50 +0800
Subject: [PATCH] perf: do a binary search for kallsyms

Signed-off-by: xh4n3 <xyn1016@gmail.com>
---
 pkg/exporter/bpfutil/kallsyms.go      | 50 ++++++++++++++++++---------
 pkg/exporter/bpfutil/kallsyms_test.go | 20 +++++++++++
 2 files changed, 54 insertions(+), 16 deletions(-)
 create mode 100644 pkg/exporter/bpfutil/kallsyms_test.go

diff --git a/pkg/exporter/bpfutil/kallsyms.go b/pkg/exporter/bpfutil/kallsyms.go
index 4fc182ea..1533dd4e 100644
--- a/pkg/exporter/bpfutil/kallsyms.go
+++ b/pkg/exporter/bpfutil/kallsyms.go
@@ -87,25 +87,43 @@ func GetSymPtFromBpfLocation(pt uint64) (*KernelSymbol, error) {
 	if ok {
 		return &sym, nil
 	}
-	if pt > kallsyms[len(kallsyms)-1].start {
-		return nil, errors.New("addr out of range")
+	// since getAllSyms is already sorted, we can do a binary search here
+	var i, j, mid int
+	var midVal uint64
+	j = len(kallsyms) - 1
+	found := -1
+	for i < j {
+		mid = i + (j-i)/2
+		midVal = kallsyms[mid].start
+		if pt < midVal {
+			j = mid
+		} else if pt > midVal {
+			i = mid + 1
+		} else {
+			found = mid
+			break
+		}
 	}
-
-	for idx := range kallsyms {
-		if kallsyms[idx].start <= pt && kallsyms[idx+1].start > pt {
-			ks := KernelSymbol{
-				start:      kallsyms[idx].start,
-				symboltype: kallsyms[idx].symbol,
-				symbol:     kallsyms[idx].symbol,
-				offset:     int(pt - kallsyms[idx].start),
-				module:     kallsyms[idx].module,
-			}
-			locationCache.Add(pt, ks)
-			return &ks, nil
+	if found == -1 {
+		if i >= 1 && pt > kallsyms[i-1].start && pt < kallsyms[i].start {
+			found = i - 1
+		}
+		if pt >= kallsyms[i].start {
+			found = i
 		}
 	}
-
-	return nil, errors.New("addr not found")
+	if found == -1 {
+		return nil, errors.New("addr not found")
+	}
+	ks := KernelSymbol{
+		start:      kallsyms[found].start,
+		symboltype: kallsyms[found].symbol,
+		symbol:     kallsyms[found].symbol,
+		offset:     int(pt - kallsyms[found].start),
+		module:     kallsyms[found].module,
+	}
+	locationCache.Add(pt, ks)
+	return &ks, nil
 }
 
 func getAllSyms() error {
diff --git a/pkg/exporter/bpfutil/kallsyms_test.go b/pkg/exporter/bpfutil/kallsyms_test.go
new file mode 100644
index 00000000..e4005198
--- /dev/null
+++ b/pkg/exporter/bpfutil/kallsyms_test.go
@@ -0,0 +1,20 @@
+package bpfutil
+
+import (
+	"math/rand"
+	"testing"
+	"time"
+)
+
+func TestGetSymPtFromBpfLocation(t *testing.T) {
+	now := time.Now()
+	for i := 0; i < len(kallsyms)-1; i++ {
+		offset := rand.Intn(100)
+		_, err := GetSymPtFromBpfLocation(kallsyms[i].start + uint64(offset))
+		if err != nil {
+			t.Fatal("failed to get symbol point", kallsyms[i], err)
+		}
+	}
+	t1 := time.Now()
+	t.Logf("time cost: %v\n", t1.Sub(now))
+}