如何当标杆缓存失效？ [英] How to invalidate cache when benchmarking?
问题描述
我有这样的code，即交换UsingAs和UsingCast的订单时，他们的表现也交换。
I have this code, that when swapping the order of UsingAs and UsingCast, their performance also swaps.
using System;
using System.Diagnostics;
using System.Linq;
using System.IO;
class Test
{
const int Size = 30000000;
static void Main()
{
object[] values = new MemoryStream[Size];
UsingAs(values);
UsingCast(values);
Console.ReadLine();
}
static void UsingCast(object[] values)
{
Stopwatch sw = Stopwatch.StartNew();
int sum = 0;
foreach (object o in values)
{
if (o is MemoryStream)
{
var m = (MemoryStream)o;
sum += (int)m.Length;
}
}
sw.Stop();
Console.WriteLine("Cast: {0} : {1}", sum,
(long)sw.ElapsedMilliseconds);
}
static void UsingAs(object[] values)
{
Stopwatch sw = Stopwatch.StartNew();
int sum = 0;
foreach (object o in values)
{
if (o is MemoryStream)
{
var m = o as MemoryStream;
sum += (int)m.Length;
}
}
sw.Stop();
Console.WriteLine("As: {0} : {1}", sum,
(long)sw.ElapsedMilliseconds);
}
}
输出：
As: 0 : 322
Cast: 0 : 281
在做这个...
UsingCast(values);
UsingAs(values);
......结果这样：
...Results to this:
Cast: 0 : 322
As: 0 : 281
这样当眼前这个...
When doing just this...
UsingAs(values);
......结果这样：
...Results to this:
As: 0 : 322
当这样做只是这：
UsingCast(values);
......结果这样：
...Results to this:
Cast: 0 : 322
除了独立运行的他们，如何的无效缓存，以便被基准将不会收到第一个code的缓存内存第二code？
Aside from running them independently, how to invalidate the cache so the second code being benchmarked won't receive the cached memory of first code?
标杆不谈，只是喜欢一个事实，即现代处理器做缓存魔法： - ）
Benchmarking aside, just loved the fact that modern processors do this caching magic :-)
至于建议试试这个快code（据说）...
As advised to try this faster code(supposedly)...
static void UsingAsAndNullTest(object[] values)
{
Stopwatch sw = Stopwatch.StartNew();
int sum = 0;
foreach (object o in values)
{
var m = o as MemoryStream;
if (m != null)
{
sum += (int)m.Length;
}
}
sw.Stop();
Console.WriteLine("As and null test: {0} : {1}", sum,
(long)sw.ElapsedMilliseconds);
}
...结果是这样的：
...The result is this:
As and null test: 0 : 342
比两个codeS上面放缓
Slower than the two codes above
：
诚如手每个例程自己的副本...
As advised to hand each routine their own copy...
static void UsingAs(object[] values)
{
object[] a = values.ToArray();
Stopwatch sw = Stopwatch.StartNew();
int sum = 0;
foreach (object o in a)
{
if (o is MemoryStream)
{
var m = o as MemoryStream;
sum += (int)m.Length;
}
}
sw.Stop();
Console.WriteLine("As: {0} : {1}", sum,
(long)sw.ElapsedMilliseconds);
}
static void UsingCast(object[] values)
{
object[] a = values.ToArray();
Stopwatch sw = Stopwatch.StartNew();
int sum = 0;
foreach (object o in a)
{
if (o is MemoryStream)
{
var m = (MemoryStream)o;
sum += (int)m.Length;
}
}
sw.Stop();
Console.WriteLine("Cast: {0} : {1}", sum,
(long)sw.ElapsedMilliseconds);
}
...输出：
Cast: 0 : 282
As: 0 : 282
现在他们有相同的效果，由于莱姆斯！
Now they have the same results, thanks Remus!
运行演作为独立的，他们也产生同样的结果（即282）。现在，为什么他们成为的更快（从322到282毫秒）时，他们都交给各自为阵的副本，我什么都做不了了吧:-)那完全是另一回事
Running Cast and As independently, they also yield the same result(i.e. 282). Now, as for why they become faster (from 322 down to 282 milliseconds) when they are handed their own copy of array, I can't make anything out of it :-) That's entirely another story
推荐答案
如果你要拿出照片的L2缓存和TLB缺失则只需拨打一个不同的MemoryStream相同尺寸的第二次测试。
If you want to take out of the picture the L2 cache and the TLB misses then simply call the second test on a different MemoryStream of the same size.
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