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SubjectRe: [PATCH RESEND] timer stats: reset entries when disable the timer usage statistics
On 10/09/2013 09:35 PM, Ingo Molnar wrote:
> * Dong Zhu <bluezhudong@gmail.com> wrote:
>
>> From f41628c61d8a9172677ba33a55b61e37ce28f7a6 Mon Sep 17 00:00:00 2001
>> From: Dong Zhu <bluezhudong@gmail.com>
>> 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.


Good point. I misunderstood the patch and thought it was an issue that
the statistics are never cleared even if the collection was disabled,
but looking closer I see we clear on enable (if we were disabled). So
yes, this change doesn't seem right.



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

Agreed.

thanks
-john


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