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

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Message-ID: <4A6834EA.3070303@cn.fujitsu.com>
Date:	Thu, 23 Jul 2009 18:01:14 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
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



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?

If so, we need to convert "expire time" into jiffies time, but
I searched ways for this type of converting but found nothing.

I'm afraid it's hard to do as below example:
  insmod-3821  [001]  3192.239335: hrtimer_start: timer=d08a1480  expires=1245162841000000000 ns
  <idle>-0     [001]  3201.506127: hrtimer_expire: timer=d08a1480

We can't convert 1245162841000000000ns to jiffies if we don't know
the xtime/wall_to_monotonic at hrimter_start.
And the expire time that got by _start() maybe wrong because user
can change time of day between hrtimer_start() and hrtimer_expire().

What your opinion?

> 
> 
> 
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