From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 30 May 2011 09:03:22 +0200 From: Pavel Machek Message-ID: <20110530070322.GA3248@domain.hid> References: <4DDE8DC9.2020905@domain.hid> <4DDF475A.5080504@domain.hid> <4DDFB30F.8000003@domain.hid> <4DDFB780.4010009@domain.hid> <4DDFBDCD.4040809@domain.hid> <4DDFEDA2.40206@domain.hid> <4DDFF74E.2000400@domain.hid> <4DE1078D.3090503@domain.hid> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4DE1078D.3090503@domain.hid> Subject: Re: [Xenomai-help] Huge clock drift List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: xenomai@xenomai.org On Sat 2011-05-28 16:32:45, Jan Kiszka wrote: > On 2011-05-27 21:11, Gilles Chanteperdrix wrote: > > On 05/27/2011 08:29 PM, Jonas Witt wrote: > >> Sorry, I missed the NTP-part. I am not using NTP. Just plain timer > >> queries on a single system. > >> > >> My clock source is tsc which is the same for Xenomai I suppose. > >> > >> I wonder how a Xenomai task, even if it occupies 50% or even 90% of a 4 > >> milliseconds time slice can interfere with the tsc. The tsc is not > >> incremented via an interrupt, is it? But I do not know much about the > >> inner workings of these functions. > > > > The problem is not the clocksource, the problem is the timer interrupt. > > The kernel expects 1 timer tick every millisecond. > > Not on archs that are CONFIG_NO_HZ capable. Umm. NO_HZ is only active while system is idle. Kernel will still expect the periodic ticks when CPU is busy.... (I'm not sure how the compensation works; perhaps it can compensate even while busy..) Pavel