linux-kernel - Re: [PATCH 0/3] Add walltime support for ring-buffer

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Date:	Mon, 3 Aug 2009 09:22:55 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Zhaolei <zhaolei@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] Add walltime support for ring-buffer

* KOSAKI Motohiro <kosaki.motohiro@...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
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