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Re: Clock Source in hrtimer

To: wu zhangjin <wuzhangjin@gmail.com>
Subject: Re: Clock Source in hrtimer
From: "wilbur.chan" <wilbur512@gmail.com>
Date: Mon, 16 Aug 2010 00:00:03 +0800
Cc: Linux MIPS Mailing List <linux-mips@linux-mips.org>
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Hi wu,

2010/8/15 wu zhangjin <wuzhangjin@gmail.com>:

>
> don't worry about it, the timekeeper solves it:
>
> kernel/time/timekeeping.c
>
> The r4k timer in most of the MIPS variants also only has a 32bits
> counter register, no problem with it:
>
> arch/mips/kernel/csrc-r4k.c
> arch/mips/kernel/cevt-r4k.c
>
> does  xlr 732 also use such a timer (with MIPS count & compare
> registers of coprocessor0)?
>

yes, xlr732  use these two registers to generate timer interrupt,
with a frequency of 1GHZ



> If you need to get the time with high resolution, please use:
> getnstimeofday(), this function will return a linear time with the
> help of timekeeper(timekeeping_get_ns).
>


1)  So hrtimer is based on  xtime,

If CONFIG_NO_HZ is set , would xtime be updated on time and correctly ?


2) some question about __get_nsec_offset :

               /* read clocksource: */
        cycle_now = clocksource_read(clock);

        /* calculate the delta since the last update_wall_time: */
        cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;



if   cycle_now  is smaller than clock->cycle_last , say , cycle_now =
3 ,    cycle->cycle_last = 2^32-1 ,  then

cycle_delta  = 3 - (2^32-1)  =  ?


> Regards,
> Wu Zhangjin
>

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