From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <48E8C1BC.3050800@domain.hid> Date: Sun, 05 Oct 2008 15:31:40 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <48E8AFB4.4040208@domain.hid> <48E8B29D.5040705@domain.hid> <48E8B704.8030403@domain.hid> <48E8B91B.1060502@domain.hid> <48E8BF4A.2030409@domain.hid> In-Reply-To: <48E8BF4A.2030409@domain.hid> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig5B07AE697670C2EC93D06595" Sender: jan.kiszka@domain.hid Subject: Re: [Xenomai-core] [Xenomai-commits] r4210 - in /trunk: ChangeLog src/skins/native/task.c List-Id: "Xenomai life and development \(bug reports, patches, discussions\)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: xenomai-core This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig5B07AE697670C2EC93D06595 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Gilles Chanteperdrix wrote: > Gilles Chanteperdrix wrote: >> Jan Kiszka wrote: >>> Gilles Chanteperdrix wrote: >>>> Jan Kiszka wrote: >>>>> Gilles Chanteperdrix wrote: >>>>>> Author: gch >>>>>> Date: Sat Oct 4 23:11:09 2008 >>>>>> New Revision: 4210 >>>>>> >>>>>> URL: http://svn.gna.org/viewcvs/xenomai?rev=3D4210&view=3Drev >>>>>> Log: >>>>>> Call __real_pthread_setschedparam in order to inform the libc of t= he scheduling parameters change. >>>>> Well, I dropped this idea after realizing that it will kick us out = of >>>>> primary mode in all cases. This change is an improvement (/wrt Linu= x >>>>> scheduling accuracy) for borderline threads, but it will cause >>>>> regressions for primary-only threads. I have no idea right now how = to >>>>> make both happy, at least without explicit pthread_setschedparam >>>>> invocations by the user application. >>>> Well, we discussed this on the xenomai mailing list, you did not ans= wer, >>>> so we assumed you agreed. >>> I do not find any hint in that thread that we agreed on changing the >>> implementation. Rather I took back my suggestion to do it like #4210.= >>> And you proposed to install some signal for syncing glibc /wrt >>> priorities. When changing something, then I would say explore this pa= th >>> first. >> We are used to hear you when you do disagree... So, since you did not >> answer Philippe mail who said "it is certainly debatable", we assumed >> you agreed. But we certainly were wrong. I may have misunderstood that this early statement in the discussion was still valid after we dug deeper into the topic. >> >>> Turning rt_task_set_priority into secondary-mode service is a critica= l >>> change, and only the last resort if we consider its current >>> implementation as totally broken - I wouldn't say it is like that. It= 's >>> partially and, unfortunately, silently broken, ie. lacking documentat= ion >>> about its limitations. But its perfectly OK for primary-only users. >> No, an important invariant of Xenomai is that the priority scales are >> synchronized between Xenomai and Linux. So, if Linux does not see the >> same priority as Xenomai, the implementation is broken. Imagine for >> instance that your primary-only thread posts an NPTL semaphore, knowin= g >> that a switch will not occur so that it will not leave primary mode. I= f >> the glibc does not see the correct priority, then a mode switch may >> occur whereas it should not. This is a bit far-fetched, but who knows >> what else may happen if the priorities are not synchronized. We >> absolutely want the priorities to be synchronized. I understand the deep desire to keep the priorities in sync for those threads that go to secondary mode (or at least accept occasional switches= ). But no one will (OK: should) seriously build a primary-only design based on assumptions about the glibc locking and syscall behavior. Practice teaches that this is doomed to break - at latest on next glibc update (or what other standard third-party lib). Primary-only means only safe Xenomai services or well-audited library calls. So turning some Xenomai service into an unsafe one remains a critical step, even if it fixes other use cases. >=20 > Ok. I am looking at the SIGWINCH change. >=20 Great, TiA. Jan --------------enig5B07AE697670C2EC93D06595 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iEYEARECAAYFAkjowb8ACgkQniDOoMHTA+nOIgCeK0tNAm6SkQaLokLzaD0j+kTo 2/4An05ikVF8lscpQHU2dvNfO6CvHUqT =m/qn -----END PGP SIGNATURE----- --------------enig5B07AE697670C2EC93D06595--