Re: [PATCH v2] timer stats: add a 'status' line to timer usagestatistics

[Dong Zhu]

Hi Ingo and John,

On Thu, Oct 10, 2013 at 06:35:19AM +0200, Ingo Molnar wrote:
> 
> * Dong Zhu <bluezhudong@xxxxxxxxx> wrote:
> 
> > From f41628c61d8a9172677ba33a55b61e37ce28f7a6 Mon Sep 17 00:00:00 2001
> > From: Dong Zhu <bluezhudong@xxxxxxxxx> 
> > Date: Thu, 10 Oct 2013 10:38:13 +0800
> > 
> > When we stop timer statistics collection (via echo 0 > 
> > /proc/timers_stats), the statistics data is still exported as if it were 
> > correct, which can cause applicaitons to misuse the statistics.
> 
> What misuse do you mean?
> 
> > This patch resets the statistics when we stop collecting them, to avoid 
> > this problem.
> 
> Well, this loses the handy 'snapshot' property of /proc/timer_stats. 
> Before this change one could do:
> 
> 	echo 1 > /proc/timers_stats
> 	sleep 60 # run system workload
> 	echo 0 > /proc/timers_stats
> 
> and examine the 1-minute collection result without it changing. Your 
> change, if I understand it correctly, zeroes it all out.

Yes, I am wrong about it. Thanks for pointing this out and pretty sorry
for confusing you John.

> 
> Instead of this change I'd suggest adding a 'status' line, with two 
> outputs:
> 
> 	Status: collection active
> 
> 	Status: collection disabled
> 

Agree, I modified this patch and resubmited it again, Could you help
reviewing it again ? Thanks !