Messages in this thread | | | From | Zhaoyang Huang <> | Date | Mon, 20 Jun 2016 09:14:58 +0800 | Subject | 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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