linux-kernel - Re: Unified tracing buffer

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Message-Id: <20080924025457.DC24.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Wed, 24 Sep 2008 02:59:37 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com, Martin Bligh <mbligh@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Steven Rostedt <rostedt@...dmis.org>, od@...ell.com,
	"Frank Ch. Eigler" <fche@...hat.com>,
	systemtap-ml <systemtap@...rces.redhat.com>
Subject: Re: Unified tracing buffer

> > I can't imazine a merit of the single-channel mode.
> > Could you please explain it?
> 
> Actually, single-channel mode is for not-frequently event tracing.
> At least systemtap case, sometimes we just want to collect data
> and watch it periodically(as like as 'top'). Or, just monitoring
> errors as additional printk. in these cases, overhead is not so
> important.
> 
> I think the main reason of using single-channel mode is simplicity of
> userspace reader. We can use 'cat' or 'tail' to read the buffer on-line.
> I'm not sure how much overhead ftrace-like buffer merging routine has,
> but if kernel provides an interface which gives us single-merged buffer
> image(like ftrace buffer), we are grad to use it. :-)

Yup, I also think it is better.

Thanks.



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