From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4DE1078D.3090503@domain.hid> Date: Sat, 28 May 2011 16:32:45 +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> In-Reply-To: <4DDFF74E.2000400@domain.hid> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigB21159599B1FBEE81479B02C" 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: Gilles Chanteperdrix , Jonas Witt Cc: xenomai@xenomai.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigB21159599B1FBEE81479B02C Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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=20 >> 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=20 >> milliseconds time slice can interfere with the tsc. The tsc is not=20 >> incremented via an interrupt, is it? But I do not know much about the = >> inner workings of these functions. >=20 > 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. > When you run a > real-time task during 2 milliseconds and prevent the kernel from > receiving the timer interrupts, you certainly disrupt its timekeeping. > If you want to do this, switch the Linux kernel frequency (CONFIG_HZ) t= o > 100. Time keeping can perfectly bridge a lot of missing ticks as far as the underlying clocksource allows. And that's quite a bit with the x86 TSC. I wonder if the TSC is sufficiently stable here. Forgot to disable CONFIG_CPU_FREQ? How does your .config look like? Jan --------------enigB21159599B1FBEE81479B02C 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/ iEYEARECAAYFAk3hB5EACgkQitSsb3rl5xSiaACfTOBIieZcs9yAbuiH+ym6cfU3 BYkAniUEn1/YOVFQgJDFNYmjFD2TC8qK =lDFR -----END PGP SIGNATURE----- --------------enigB21159599B1FBEE81479B02C--