TONT 37003 追寻更加迅速的syscall陷阱

原文链接：https://devblogs.microsoft.com/oldnewthing/20041215-00/?p=37003

The performance of the syscall trap gets a lot of attention.

有关 syscall 陷阱的效率问题吸引了很多人的注意。

I was reminded of a meeting that took place between Intel and Microsoft over fifteen years ago. (Sadly, I was not myself at this meeting, so the story is second-hand.)

我想起了十五年前 Intel 和微软之间的一次会议。（很遗憾当时我没有亲自在场，所以接下来的故事是转述的。）

Since Microsoft is one of Intel’s biggest customers, their representatives often visit Microsoft to show off what their latest processor can do, lobby the kernel development team to support a new processor feature, and solicit feedback on what sort of features would be most useful to add.

鉴于微软是 Intel 最大的客户之一，Intel 的代表经常到访微软，炫耀他们最新款的处理器的能力，游说内核开发团队支持一项新的处理器功能，并且征求有关有意向添加到处理器中的、最有用的功能类别。

At this meeting, the Intel representatives asked, “So if you could ask for only one thing to be made faster, what would it be?”

在那次会议上，Intel 的代表问道，『如果只有一件事可以提速，你们希望是什么呢？』

Without hesitation, one of the lead kernel developers replied, “Speed up faulting on an invalid instruction.”

内核团队的一位领头开发者不假思索地回答道：『执行无效指令时的出错再快一点。』

The Intel half of the room burst out laughing. “Oh, you Microsoft engineers are so funny!” And so the meeting ended with a cute little joke.

会议室里 Intel 一侧的人们大笑起来，『哎呀，你们微软的工程师可真有意思！』会议在这个小而有趣的玩笑中收场了。

After returning to their labs, the Intel engineers ran profiles against the Windows kernel and lo and behold, they discovered that Windows spent a lot of its time dispatching invalid instruction exceptions. How absurd! Was the Microsoft engineer not kidding around after all?

等回到实验室之后，Intel 的工程师们对 Windows 的内核进行了测评，出乎意料地发现 Windows 花了大量的时间来调度无效的指令异常。这也太荒谬了吧！微软的那些工程师原来并不是在开玩笑吗？

No he wasn’t.

还真不是。

It so happens that on the 80386 chip of that era, the fastest way to get from V86-mode into kernel mode was to execute an invalid instruction! Consequently, Windows/386 used an invalid instruction as its syscall trap.

原来在那个时代的 80386 处理器上，从虚拟8086模式切换到内核模式最快的方法，正是执行一个无效的指令！因此，Windows/386 将无效指令作为了 syscall 的陷阱。

What’s the moral of this story? I’m not sure. Perhaps it’s that when you create something, you may find people using it in ways you had never considered.

至于这个故事教给我们的道理是什么，我并不太确定。大概是当你创造了一项事物时，你会发现人们会用你从未考虑过的方式去使用它。