linux-kernel - Re: [-mm patch] x86_64 GTOD: offer scalable vgettimeofday

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Message-Id: <200702011301.51834.ak@suse.de>
Date:	Thu, 1 Feb 2007 13:01:51 +0100
From:	Andi Kleen <ak@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	jbohac@...e.cz, linux-kernel@...r.kernel.org,
	Vojtech Pavlik <vojtech@...e.cz>, arjan@...radead.org,
	tglx@...utronix.de, johnstul@...ibm.com,
	Andrew Morton <akpm@...l.org>
Subject: Re: [-mm patch] x86_64 GTOD: offer scalable vgettimeofday

On Thursday 01 February 2007 12:46, Ingo Molnar wrote:
> 
> * jbohac@...e.cz <jbohac@...e.cz> wrote:
> 
> > Inter-CPU monotonicity can not, however, be guaranteed in a vsyscall, 
> > so vsyscall is not used by default. [...]
> 
> note that this is not actually the case. My patch below, ontop of -mm, 
> implements a fully monotonic gettimeofday as an optional vsyscall 
> feature.
> 
> The 'price' paid for it is lower resolution - but it's still good for 
> those benchmarking TPC-C runs - and /alot/ simpler. It's also quite a 
> bit faster than any TSC based vgettimeofday, because it doesnt have to 
> do an RDTSC (or RDTSCP) instruction nor any approximation of the time.

I believe that should be also a separate clock_gettime() CLOCK_ 

Global settings for these things are bad. Even if you run TPC-C you don't
want your other programs that rely on monotonic time to break.

-Andi

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