From mboxrd@z Thu Jan 1 00:00:00 1970 From: Helge Deller Subject: Re: timerfd_settime/timerfd_gettime issue ? Date: Tue, 29 Dec 2015 21:13:30 +0100 Message-ID: <5682E96A.5040008@gmx.de> References: <567E8766.6020707@gmx.de> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Cc: Linux Kernel Development , linux-parisc To: Thomas Gleixner Return-path: In-Reply-To: List-ID: List-Id: linux-parisc.vger.kernel.org On 29.12.2015 10:44, Thomas Gleixner wrote: > On Sat, 26 Dec 2015, Helge Deller wrote: >> I see a strange behavior on the parisc platform, for which I'm not sure if >> it's intended or if there is a bug somewhere. > >> The program calls timerfd_settime() and sets a timer (e.g. sec=0, nsec=100000000). >> Directly after setting the timer it calls timerfd_gettime() and receives >> (sec=0, nsec=103914413). >> The second nsec is higher than the initial nsec value which was set. >> >> Does timerfd_settime() maybe tries to add the initial time it takes to start >> the timer? >> >> Any idea or hint? > > Yes. This is a fallout from the power aware batching magic. Interesting that > nobody noticed this within 7 years. > > Does the patch below fix your issue? 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) Helge > diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h > index 76dd4f0da5ca..0f4a3e8734f1 100644 > --- a/include/linux/hrtimer.h > +++ b/include/linux/hrtimer.h > @@ -268,7 +268,7 @@ static inline s64 hrtimer_get_expires_ns(const struct hrtimer *timer) > > static inline ktime_t hrtimer_expires_remaining(const struct hrtimer *timer) > { > - return ktime_sub(timer->node.expires, timer->base->get_time()); > + return ktime_sub(timer->_softexpires, timer->base->get_time()); > } > > static inline ktime_t hrtimer_cb_get_time(struct hrtimer *timer)