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Date: Mon, 3 Aug 2009 09:22:55 +0200
From: Ingo Molnar <mingo@elte.hu>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
       Steven Rostedt <rostedt@goodmis.org>, Zhaolei <zhaolei@cn.fujitsu.com>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/3] Add walltime support for ring-buffer
Message-ID: <20090803072255.GB27581@elte.hu>
References: <20090728103227.D7FB.A69D9226@jp.fujitsu.com> <20090728015351.GF5147@nowhere> <20090728105931.D801.A69D9226@jp.fujitsu.com>
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* KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:

> It can. but I don't think it is sufficient. On flight recorder 
> use-case, The tracing run more than one year. And, Administrator 
> only see last N sec log. (previous logs were overwritten by 
> ring-buffer go-around)

That's definitely something we want to enable ASAP.

I'm wondering why a single u64 timestamp is not enough to express 
the full, absolute range of time elapsed since bootup, in 
nanoseconds.

That would make walltime a matter of pretty-printing only - we'd 
have to convert the u64 nsec timestamp into a walltime format, 
right?

In fact we could change all the timestamps to be standardized along 
'nanoseconds elapsed since 1970' or so - not nanoseconds since the 
last bootup. That still fits just fine within 64 bits - u64 
nanoseconds has a scope of 500+ years.

	Ingo