linux-kernel - Re: [patch, v2.6.22-rc6] sys

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Message-ID: <20070627002208.GB6670@v2.random>
Date:	Wed, 27 Jun 2007 02:22:08 +0200
From:	Andrea Arcangeli <andrea@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	John Stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch, v2.6.22-rc6] sys_time() speedup

On Tue, Jun 26, 2007 at 10:14:40AM -0700, Andrew Morton wrote:
> On my machine, time(2) doesn't do any syscall at all - it uses the vsyscall
> page.  I'd be surprised if a database uses sys_time() either.

Large boxes unfortunately can't always use vsyscalls...  that's a real
pity. I also had to disable the vsyscalls64 to generate some number.

I think there shall be a perfectly accurate but not monotone mode for
gettimeofday so we can enable rdtscp (via sysctl or/and prctl). Aware
apps can enable the prctl, aware or brave admins can turn on the
sysctl. Vojtech and others should have proper patches to merge for
this.
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