linux-kernel - Re: [PATCH v3 3/4] ftrace: add tracepoint for hrtimer

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Message-Id: <1248343661.27058.1722.camel@twins>
Date:	Thu, 23 Jul 2009 12:07:41 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Zhaolei <zhaolei@...fujitsu.com>, kosaki.motohiro@...fujitsu.com,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Anton Blanchard <anton@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/4] ftrace: add tracepoint for hrtimer

On Thu, 2009-07-23 at 18:01 +0800, Xiao Guangrong wrote:
> 
> Peter Zijlstra wrote:
> 
> > OK, so what you want to measure is the time of the actual callback
> > happening (hrtimer_entry) vs that where you would have expected it to
> > happen (hrtimer_start + delay), right?
> > 
> 
> Yes
> 
> > So what's wrong with printing the expected expiration time in the
> > hrtimer_start tracepoint in the cheap clock units?
> > 
> 
> Is "cheap clock units" means jiffies time?

Nah, something like cpu_clock() which is monotonic per-cpu and should
have high resolution where available.
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