linux-kernel - Re: Sysenter crash with Nested Task Bit set

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Date:	Mon, 18 Sep 2006 17:06:50 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	Andrew Morton <akpm@...l.org>,
	Chuck Ebbert <76306.1226@...puserve.com>,
	In Cognito <defend.the.world@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>
Subject: Re: Sysenter crash with Nested Task Bit set


* Linus Torvalds <torvalds@...l.org> wrote:

> And sysenter really is very special because of the weak trap 
> semantics. Damn. We could either fix it in the sysenter code-path, or 
> in the task-switch one, and both of them are timing-critical, but task 
> switching perhaps just a tad less so.

agreed. Context-switching is 10 times less frequent on most workloads 
than syscalls, so if it takes 10 cycles in the context-switch path to 
eliminate a 1 cycle overhead in the syscall-entry path then we are still 
break-even on average. In this case the overhead is similar i think, so 
the switch_to() fix is preferable.

	Ingo
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