linux-kernel - Re: [PATCH v4 0/6] Micro-optimize vclock

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Date:	Tue, 17 May 2011 21:27:01 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andy Lutomirski <luto@....EDU>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Borislav Petkov <bp@...64.org>
Subject: Re: [PATCH v4 0/6] Micro-optimize vclock_gettime


* Andy Lutomirski <luto@....EDU> wrote:

> It's even easier than that: there are no syscall numbers involved.  There are 
> four separate entry points, one for each vsyscall.
> 
> (It turns out that one of them has been broken and just segfaults since 2008 
> (a4928cff), so we only have to emulate three of them.)
> 
> On KVM on Sandy Bridge, I can emulate a vsyscall that does nothing in 400ns 
> or so.  I'll try to make this code emulate real vsyscalls over the weekend.  

Very nice!

> This was much easier than I expected.

Hey, looking back at a working patch always makes it seem easy ;-)

Thanks,

	Ingo
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