Re: timerfd_settime/timerfd_gettime issue ?

[Thomas Gleixner]

On Tue, 29 Dec 2015, Helge Deller wrote:
> No, the patch below doesn't help.
> 
> I still see:
> [  644.916000] timerfd_settime: interval (sec=0, nsec=100000000) it_value (sec=0, nsec=100000000) 
> [  645.024000] timerfd_gettime: interval (sec=0, nsec=100000000) it_value (sec=0, nsec=103029949) 
> 

Right. It can't help. Sorry for the distraction.

Looking deeper I found the issue. It's caused by CONFIG_TIME_LOW_RES. See the
comment in hrtimer_start_range_ns(). We round the expiry time to the next
jiffies period to avoid short timeouts. Assuming you are running with HZ=250
this is exactly 4ms. So that's where your extra time comes from.

Not sure what to do about that.

Thanks,

	tglx






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