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Date: Tue, 23 Sep 2008 14:38:00 -0000
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Masami Hiramatsu <mhiramat@redhat.com>
Subject: Re: Unified tracing buffer
Cc: kosaki.motohiro@jp.fujitsu.com, Martin Bligh <mbligh@google.com>,         Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,         Linus Torvalds <torvalds@linux-foundation.org>,         Thomas Gleixner <tglx@linutronix.de>,         Mathieu Desnoyers <compudj@krystal.dyndns.org>,         Steven Rostedt <rostedt@goodmis.org>, od@novell.com,         "Frank Ch. Eigler" <fche@redhat.com>,         systemtap-ml <systemtap@sources.redhat.com>
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> By the way, systemtap uses two modes;
> 
> - single-channel mode
>  In this mode, all cpus share one buffer channel to write and read.
>  each writer locks spinlock and write a probe-local data to buffer.
> 
> - per-cpu buffer mode
>  In this mode, we use an atomic sequential number for ordering data. If
>  user doesn't need it(because they have their own timestamps), they can
>  choose not to use that seq-number.

I can't imazine a merit of the single-channel mode.
Could you please explain it?

Because some architecture don't have fine grained timestamp?
if so, could you explain which architecture don't have it?