From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4DE34E02.6000206@domain.hid> Date: Mon, 30 May 2011 09:57:54 +0200 From: Jan Kiszka MIME-Version: 1.0 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> <20110530070322.GA3248@domain.hid> <4DE34223.8030505@domain.hid> <4DE34AA3.2090500@domain.hid> In-Reply-To: <4DE34AA3.2090500@domain.hid> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigCFE4B11EC8EBD43762A0610D" Sender: jan.kiszka@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: Jonas Witt Cc: xenomai@xenomai.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigCFE4B11EC8EBD43762A0610D Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 2011-05-30 09:43, Jonas Witt wrote: > Am 30.05.2011 09:07, schrieb Jan Kiszka: >> On 2011-05-30 09:03, Pavel Machek wrote: >>> 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..) >> See update_wall_time, the !CONFIG_ARCH_USES_GETTIMEOFFSET includes no >> fixed tick length. >> >> Again, this is also important for Linux when running over hypervisors >> which tend to miss ticks on overcommitment as well. >> >> Jan >=20 > Thanks for the active discussion of the issue. I attached my config. > CONFIG_NO_HZ is activated and I think I disabled all power management > and frequency scaling correctly. Do you think it is worth trying a > kernel with fixed Hz as Gilles suggested? Actually the 1ms Xenomai load= > seems to play at least some role in the issue. For sure, I may also be proven wrong by plain reality. In addition, enable CONFIG_PM and ACPI with the exception of ACPI_PROCESSOR. Who knows what your BIOS is doing in the absence of OS support for this. Jan --------------enigCFE4B11EC8EBD43762A0610D Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.15 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org/ iEYEARECAAYFAk3jTgIACgkQitSsb3rl5xQEcACeMj/kMjKBUPfSTP2oAx2NwuTI 63sAn05+D1VBUO/n9/Yh2zk+ffu8Yrz8 =TSUO -----END PGP SIGNATURE----- --------------enigCFE4B11EC8EBD43762A0610D--