From: Thomas Gleixner <tglx@linutronix.de>
To: Helge Deller <deller@gmx.de>
Cc: Linux Kernel Development <linux-kernel@vger.kernel.org>,
linux-parisc <linux-parisc@vger.kernel.org>
Subject: Re: timerfd_settime/timerfd_gettime issue ?
Date: Wed, 30 Dec 2015 10:57:56 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.11.1512301052520.28591@nanos> (raw)
In-Reply-To: <5682E96A.5040008@gmx.de>
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
next prev parent reply other threads:[~2015-12-30 9:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-26 12:26 Helge Deller
2015-12-29 9:44 ` Thomas Gleixner
2015-12-29 20:13 ` Helge Deller
2015-12-30 9:57 ` Thomas Gleixner [this message]
2016-01-04 22:27 ` Helge Deller
2016-01-10 20:57 ` [PATCH parisc,frv,m68k] timerfd: Fix timeout values with CONFIG_TIME_LOW_RES=y Helge Deller
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