Timers not working as expected

[Georgios Magklaras]

Hi Ankit,

How did you measure the 2500 microsecond interval?

The timeval structure should give you a proper microsecond resolution 
BUT, the accuracy of the timer is normally limited by the software clock 
(100, 250, 300, 1000 Hz). If a timer expiration value does not match a 
multiple of the jiffies you set the system clock as a kernel compilation 
option, you get rounding errors.

Also in kernels prior to 2.6.21 (where you can see the 
CONFIG_HIGH_RES_TIMERS kernel config option), you could have some 
conditions depending on system age (clock) and load or scheduler issues, 
where you see these deviations. If you switch to 2.6.21, you should get 
proper high resolution timing and if you combine that with modern (last 
3 years) hardware, you should really be able to schedule accurately down 
to microsec resolution.

GM

Best regards,

-- 
-- 
George Magklaras PhD
RHCE no: 805008309135525

Senior Systems Engineer/IT Manager
Biotechnology Center of Oslo and
the Norwegian Center for Molecular Medicine
EMBnet TMPC Chair

http://folk.uio.no/georgios




On 05/30/2012 10:10 AM, Ankit Mahawar wrote:
> Hi All,
>
> My kernel version is  2.6.14 with high resolution subsystem core having
> linux hrtimer patch  with commit id
> c0a3132963db68f1fbbd0e316b73de100fee3f08
>
> I had set a timer which expired  every 0.5 sec using setitimer api  .
>
> I  noticed that  timers were expiring fast enough at a continuous basis ,
> expiring at around 2500 micro sec interval.
>
> Has anyone encountered this scenario before  ?
>
> Please help to understand the case in which it might occur .
>
> Thanks
> Ankit
>
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