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

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Message-ID: <20110608091120.GI27166@one.firstfloor.org>
Date:	Wed, 8 Jun 2011 11:11:20 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	pageexec@...email.hu
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


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,

A pagefault is a bit faster than a virtualization intercept, but not
much and therefore too slow.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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