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Date: Thu, 16 Jan 2003 19:34:57 -0500
From: Jim Houston <jim.houston@attbi.com>
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To: Jamie Lokier <lk@tantalophile.demon.co.uk>
CC: linux-kernel@vger.kernel.org,
       high-res-timers-discourse@lists.sourceforge.net, jim.houston@ccur.com
Subject: Re: [PATCH] improved boot time TSC synchronization
References: <200301161644.h0GGitX02052@linux.local> <20030116213332.GA14040@bjl1.asuk.net>
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Jamie Lokier wrote:
> 
> It looks like not only can you synchronise with a certain accuracy,
> you can determine an upper bound on that accuracy (assuming the
> underlying CPU clocks are locked).
> 
> Maybe that figure could be put into /proc/cpuinfo?
> 
> As well as being an interesting value, it may be useful for programs
> to know the effective accuracy of `rdtsc'.
> 
> -- Jamie

Hi Jamie,

Yeah, I'd be glad to add the round-trip time to cpuinfo.  I see
this as a bogomips like metric.  It tells you how quickly you 
can move cache lines from chip to chip.

The patch currently prints the round-trip time and the max_delta.
On a Quad P4 Xeon, I got round-trip times in the 0.7 microsecond
range which is disappointing. The max_delta was almost always
zero cycles meaning that the feedback loop thinks that the TSC values
are perfectly synchronized.

Jim Houston - Concurrent Computer Corp.
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