From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4DE34223.8030505@domain.hid> Date: Mon, 30 May 2011 09:07:15 +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> In-Reply-To: <20110530070322.GA3248@domain.hid> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig676EC402474E42B5D4FCAF48" 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: Pavel Machek Cc: xenomai@xenomai.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig676EC402474E42B5D4FCAF48 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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=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 th= e=20 >>>> inner workings of these functions. >>> >>> The problem is not the clocksource, the problem is the timer interrup= t. >>> The kernel expects 1 timer tick every millisecond. >> >> Not on archs that are CONFIG_NO_HZ capable. >=20 > Umm. NO_HZ is only active while system is idle. Kernel will still > expect the periodic ticks when CPU is busy.... >=20 > (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 --------------enig676EC402474E42B5D4FCAF48 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/ iEYEARECAAYFAk3jQiUACgkQitSsb3rl5xRZNgCfdox9QGXKR5Gv7kHbFaNywPDf JWMAn3WlvRay9NvYG4inZtFt63VxI5GN =aggQ -----END PGP SIGNATURE----- --------------enig676EC402474E42B5D4FCAF48--