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

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Date:	Tue, 26 Jun 2007 16:58:25 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mark Lord <lkml@....ca>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch, v2.6.22-rc6] sys_time() speedup


* Mark Lord <lkml@....ca> wrote:

> Ingo Molnar wrote:
> >Subject: [patch] sys_time() speedup
> >From: Ingo Molnar <mingo@...e.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.

> Programs invoking sys_time() do expect it to be as accurate as 
> gettimeofday(), even if only at 1-second boundaries.

yes.

	Ingo
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