From: Andi Kleen <ak@suse.de>
To: Ingo Molnar <mingo@elte.hu>
Subject: Re: [-mm patch] x86_64 GTOD: offer scalable vgettimeofday II
Date: Thu, 1 Feb 2007 13:17:45 +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>
In-Reply-To: <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. 

BTW another comment: I was told that at least one of the big databases
wants ms resolution here. So to make your scheme work
would require a HZ=1024 regular interrupt. But that would also make
everything slower again due to CPU overhead as it was learned in the 2.4->2.6 HZ 
transition. 

So it might not actually be worth it.

-Andi

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