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Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of sleep_length

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On 17 June 2016 at 19:50, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Fri, 17 Jun 2016, Zhaoyang Huang wrote:
>> On 17 June 2016 at 17:27, Thomas Gleixner <tglx@linutronix.de> wrote:
>> > On Fri, 17 Jun 2016, Zhaoyang Huang wrote:
>> >> There should be a gap between tick_nohz_idle_enter and
>> >> tick_nohz_get_sleep_length when idle, which will cause the
>> >> sleep_length is not very precised. Change it in this patch.
>> >
>> > What kind of imprecision are we talking about? Seconds, nanoseconds or
>> > lightyears?
>> >
>> > Your changelog lacks any form of useful information.
>> >
>> sorry for the confusion. The imprecision can be caused by, for
>> example, the callback function registered for CPU_PM_ENTER, which may
>> consume a period of time within the 'idle' time. Besides, I also
>> wonder why not calc the 'sleep_length' in the
>> tick_nohz_get_sleep_length?  This value is calculated at very
>> beginning of the idle in current approach.
>
> You still are not explaining the amount of imprecision. What are you talking
> about and is it really relevant in any way or are you just trying to solve an
> acedemic issue?
>
> Thanks,
>
>         tglx
>
Indeed, it is depends on how deep the idle state is. For example, the
lightest level for my current platform is 1100us, which sums up the
entry,exit and min time. However, there is a callback which do memory
management(merge the same page) in CPU_PM_ENTER will consume at least
500us. In current approach, it cause 50% imprecision for this level of
idle state.

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[RESEND PATCH v2 1/2] power/cpuidle: enhance the precision of state select Zhaoyang Huang <zhaoyang.huang@linaro.org> - 2016-06-17 11:20 +0200
  [RESEND PATCH v2 2/2] power/idle: enhance the precision of sleep_length Zhaoyang Huang <zhaoyang.huang@linaro.org> - 2016-06-17 11:20 +0200
    Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of  sleep_length Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 11:30 +0200
      Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of sleep_length Zhaoyang Huang <zhaoyang.huang@linaro.org> - 2016-06-17 13:20 +0200
        Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of  sleep_length Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 14:00 +0200
          Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of sleep_length Zhaoyang Huang <zhaoyang.huang@linaro.org> - 2016-06-20 03:20 +0200
            Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of sleep_length Zhaoyang Huang <zhaoyang.huang@linaro.org> - 2016-06-22 05:10 +0200
              Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of  sleep_length Thomas Gleixner <tglx@linutronix.de> - 2016-06-23 09:10 +0200
                Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of sleep_length Zhaoyang Huang <zhaoyang.huang@linaro.org> - 2016-06-23 09:30 +0200
                Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of  sleep_length Thomas Gleixner <tglx@linutronix.de> - 2016-06-23 10:30 +0200
                Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of  sleep_length Thomas Gleixner <tglx@linutronix.de> - 2016-06-23 10:40 +0200
                Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of sleep_length Zhaoyang Huang <zhaoyang.huang@linaro.org> - 2016-06-23 10:50 +0200
                Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of  sleep_length Thomas Gleixner <tglx@linutronix.de> - 2016-06-23 12:20 +0200
                Re: [RESEND PATCH v2 2/2] power/idle: enhance the precision of sleep_length Zhaoyang Huang <zhaoyang.huang@linaro.org> - 2016-06-23 10:40 +0200

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