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rednoah | 10 Jul 2012 04:02
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For smp, is it possible that a timer can be run at the same time on different cpus?

Hi all:
  The kernel I use is 2.6.29-rc3 and among the timer_list function there is "add_timer_on". 
For smp, Is it possible for a timer to be run at the same time on different cpus? suppose the
following sequence:
1. a timer is being run on CPU 0, and the timer callback function use add_time_on to add itself on CPU 1;
  the expires is set to "jiffies + 0" to make it to be run as quickly as possible on CPU 1.
2. so there is chance that 2 cpus run the same timer at the same time?

I'm not sure whether the above can be true. Whether there is other way to make a time run at the same time
on different cpu?  If it can happen, the timer callback function must take smp safe into consideration.

Regards
Rednoah

 

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Mulyadi Santosa | 10 Jul 2012 07:10
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Re: For smp, is it possible that a timer can be run at the same time on different cpus?

Hi.... :)

On Tue, Jul 10, 2012 at 9:02 AM, rednoah <rednoax <at> gmail.com> wrote:
> Hi all:
>   The kernel I use is 2.6.29-rc3 and among the timer_list function there is
> "add_timer_on".
> For smp, Is it possible for a timer to be run at the same time on different
> cpus? suppose the
> following sequence:
> 1. a timer is being run on CPU 0, and the timer callback function use
> add_time_on to add itself on CPU 1;
>   the expires is set to "jiffies + 0" to make it to be run as quickly as
> possible on CPU 1.
> 2. so there is chance that 2 cpus run the same timer at the same time?

Interesting issue :)

IMHO, even though you ask for "jiffies+" a.k.a current time,
scheduling delay will make it run in the very very near future. This
is plus the fact that I know that timer is running everytime time
interrupt is receieved... so IMHO that very near future is actually
jiffies+1 (current time + (1/HZ))

I might be wrong here though :)

--

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com
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Gmane