linux-kernel - Re: clockevent questions

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Date:	Tue, 15 May 2007 10:47:52 +0200
From:	"Francis Moreau" <francis.moro@...il.com>
To:	tglx@...utronix.de
Cc:	linux-kernel@...r.kernel.org
Subject: Re: clockevent questions

Thomas,

On 5/12/07, Thomas Gleixner <tglx@...utronix.de> wrote:
> Well, it ends up in hrtimer_interrupt() and the code there finds out,
> that the next timer is not due right now, so it simply requests the same
> (absolute) time event again, which is processed by the clock events code
> and eventually limited to the max delta of the device again.
>

My timer is finally using the clockevent subsystem. Below is the
output of '/proc/timer_list':

cat /proc/timer_list
Timer List Version: v0.3
HRTIMER_MAX_CLOCK_BASES: 2
now at 64696544360531 nsecs

cpu: 0
 clock 0:
  .index:      0
  .resolution: 1 nsecs
  .get_time:   ktime_get_real
  .offset:     1179151153000000000 nsecs
active timers:
 clock 1:
  .index:      1
  .resolution: 1 nsecs
  .get_time:   ktime_get
  .offset:     0 nsecs
active timers:
 #0: <c03fde10>, tick_sched_timer, S:01
 # expires at 64696546875000 nsecs [in 2514469 nsecs]
  .expires_next   : 64696546875000 nsecs
  .hres_active    : 1
  .nr_events      : 16562163
  .nohz_mode      : 0
  .idle_tick      : 0 nsecs
  .tick_stopped   : 0
  .idle_jiffies   : 0
  .idle_calls     : 0
  .idle_sleeps    : 0
  .idle_entrytime : 0 nsecs
  .idle_sleeptime : 0 nsecs
  .last_jiffies   : 0
  .next_jiffies   : 0
  .idle_expires   : 0 nsecs
jiffies: 16485515


Tick Device: mode:     1
Clock Event Device: hrt
 max_delta_ns:   2147483647
 min_delta_ns:   1000
 mult:           206158430
 shift:          32
 mode:           3
 next_event:     64696546875000 nsecs
 set_next_event: hrt_next_event
 set_mode:       hrt_timer_setup
 event_handler:  hrtimer_interrupt

My question is about the clock resolution field which is equal to 1ns.
How is this possible since my timer's frequency is only 100Mhz ?

My 2 cents, it looks like some tabs are missing when printing the list
of hrtimers of each clock...

Thanks
-- 
Francis
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