From: Andi Kleen <ak@suse.de>
To: Ingo Molnar <mingo@elte.hu>
Subject: Re: [-mm patch] x86_64 GTOD: offer scalable vgettimeofday
Date: Thu, 1 Feb 2007 13:01:51 +0100
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Cc: jbohac@suse.cz, linux-kernel@vger.kernel.org,
       Vojtech Pavlik <vojtech@suse.cz>, arjan@infradead.org,
       tglx@linutronix.de, johnstul@us.ibm.com, Andrew Morton <akpm@osdl.org>
References: <20070201095952.589234000@jet.suse.cz> <20070201114644.GB26453@elte.hu>
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On Thursday 01 February 2007 12:46, Ingo Molnar wrote:
> 
> * jbohac@suse.cz <jbohac@suse.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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