Why the first method run is slower than after first run?

using UnityEngine;

public class InstanceTest : MonoBehaviour {
public int cnt; public bool startTest1 = false; public bool startTest2 = false;

 void Update()
 {
     if (startTest1)
         Test1(cnt);
     if (startTest2)
         Test2(cnt);
 }
 void Test1(int cnt)
 {
     float a;
     for (int i = 0; i < cnt; i++)        
         a = 1f + 1f;        
 }
 static void Test2(int cnt)
 {
     float a;
     for (int i = 0; i < cnt; i++)        
         a = 1f + 1f;        
 }

}

On profiler

when play the code, InstanceTest.Update()'s CPU Time is hiccup when execute Test1() and Test2() on first time. Is it cause of Mono JIT? I tried to use RuntimeHelpers.PrepareMethod() on Awake() to preload method but it wasn't work