＆QUOT; CPUID＆QUOT;前＆QUOT; RDTSC＆QUOT; [英] "cpuid" before "rdtsc"

问题描述

有时我遇到code与 RDTSC 读取TSC指令，但电话 CPUID 权利之前。

Sometimes I encounter code that reads TSC with rdtsc instruction, but calls cpuid right before.

为什么叫 CPUID 有必要吗？我意识到这可能是与有TSC的值不同的内核，但什么究竟的，当你调用序列中的这两个指令会发生什么？

Why is calling cpuid necessary? I realize it may have something to do with different cores having TSC values, but what exactly happens when you call those two instructions in sequence?

推荐答案

这是为prevent乱序执行。请参见这里的全部细节，下面的相关位：

It's to prevent out-of-order execution. See here for full details, relevant bit below:

奔腾Pro和奔腾II处理器支持乱序执行指令可以在另一个顺序编程你他们执行。这可能是错误的来源，如果不照顾。

The Pentium Pro and Pentium II processors support out-of-order execution instructions may be executed in another order as you programmed them. This can be a source of errors if not taken care of.

要prevent这个程序员必须序列化指令队列。这可以通过RDTSC指令之前插入像CPUID指令序列化指令来实现。

To prevent this the programmer must serialize the the instruction queue. This can be done by inserting a serializing instruction like CPUID instruction before the RDTSC instruction.

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