From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754362AbbL3J66 (ORCPT ); Wed, 30 Dec 2015 04:58:58 -0500 Received: from www.linutronix.de ([62.245.132.108]:44117 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752407AbbL3J6x (ORCPT ); Wed, 30 Dec 2015 04:58:53 -0500 Date: Wed, 30 Dec 2015 10:57:56 +0100 (CET) From: Thomas Gleixner To: Helge Deller cc: Linux Kernel Development , linux-parisc Subject: Re: timerfd_settime/timerfd_gettime issue ? In-Reply-To: <5682E96A.5040008@gmx.de> Message-ID: References: <567E8766.6020707@gmx.de> <5682E96A.5040008@gmx.de> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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