linux-kernel - Re: [PATCH v5 8/9] x86-64: Emulate legacy vsyscalls

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Message-ID: <4DEF424F.2351.1C15AD40@pageexec.freemail.hu>
Date:	Wed, 08 Jun 2011 11:35:11 +0200
From:	pageexec@...email.hu
To:	Andi Kleen <andi@...stfloor.org>
CC:	Ingo Molnar <mingo@...e.hu>, Andrew Lutomirski <luto@....edu>,
	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Jesper Juhl <jj@...osbits.net>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Jan Beulich <JBeulich@...ell.com>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	Mikael Pettersson <mikpe@...uu.se>,
	Andi Kleen <andi@...stfloor.org>,
	Brian Gerst <brgerst@...il.com>,
	Louis Rilling <Louis.Rilling@...labs.com>,
	Valdis.Kletnieks@...edu
Subject: Re: [PATCH v5 8/9] x86-64: Emulate legacy vsyscalls

On 8 Jun 2011 at 11:11, Andi Kleen wrote:

> There's clear evidence that any kind of exception in gettimeofday()/time()
> is too slow. A few years ago gtod() had CPUID which lead to intercepts
> with many hypervisors. This turned out to be a unacceptable slowdown,
> so it was fixed,

yes, i don't think anyone claimed any performance improvements from moving
away from the vsyscall page into taking exceptions ;). i think everyone
considers this as a stop-gap compatibility measure only that will be less
and less relevant and eventually may even go away as time progresses and
linux systems begin to fully rely on the vdso instead.

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