Subject: Re: [patch, v2.6.22-rc6] sys_time() speedup
From: john stultz <johnstul@us.ibm.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Mark Lord <lkml@rtr.ca>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@linux-foundation.org>,
       Thomas Gleixner <tglx@linutronix.de>
In-Reply-To: <20070626145825.GA31076@elte.hu>
References: <20070625200601.GA18980@elte.hu> <46805C4F.1050200@rtr.ca>
	 <20070626145825.GA31076@elte.hu>
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Date: Tue, 26 Jun 2007 09:59:24 -0700
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On Tue, 2007-06-26 at 16:58 +0200, Ingo Molnar wrote:
> * Mark Lord <lkml@rtr.ca> wrote:
> 
> > Ingo Molnar wrote:
> > >Subject: [patch] sys_time() speedup
> > >From: Ingo Molnar <mingo@elte.hu>
> > >
> > >improve performance of sys_time(). sys_time() returns time in seconds, 
> > >but it does so by calling do_gettimeofday() and then returning the 
> > >tv_sec portion of the GTOD time. But the data structure "xtime", which 
> > >is updated by every timer/scheduler tick, already offers HZ granularity 
> > >time.
> > 
> > How well synchronized is xtime with real-time ?
> 
> it's updated by every jiffy.

Well, NTP_INTERVAL_LENGTH to be specific which is every jiffie with one
exception: With dynticks this is a bit more complicated, and xtime is
updated only twice a second.

thanks
-john

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