From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4BB5C0BD.7080208@domain.hid> Date: Fri, 02 Apr 2010 12:02:37 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <20100401230843.GF3755@domain.hid> <4BB53566.3010601@domain.hid> <4BB53643.2080604@domain.hid> <4BB5AA44.6000006@domain.hid> <4BB5AACE.7020602@domain.hid> <4BB5B1BD.6020903@domain.hid> <4BB5B2D3.80708@domain.hid> <4BB5B7B1.3030601@domain.hid> In-Reply-To: <4BB5B7B1.3030601@domain.hid> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig6BC71034EF37C0E131FC4D9F" Sender: jan.kiszka@domain.hid Subject: Re: [Xenomai-help] New scheduler class List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: xenomai@xenomai.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig6BC71034EF37C0E131FC4D9F Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Gilles Chanteperdrix wrote: > Jan Kiszka wrote: >> Jan Kiszka wrote: >>> Gilles Chanteperdrix wrote: >>>> Jan Kiszka wrote: >>>>> Gilles Chanteperdrix wrote: >>>>>> Jan Kiszka wrote: >>>>>>> Andreas Glatz wrote: >>>>>>>> Hi Philippe, >>>>>>>> >>>>>>>> At the Xenomai Users Meeting last year I asked you if Xenomai wo= uld offer a possibility to lower the priority of certain Xenomai tasks be= low that of Linux. We need this feature since we have tasks in our RT app= lication which should only run when Linux is idle (A statistics collectio= n task which part of the RT application and hard to isolate from this app= lication). >>>>>>>> >>>>>>> What prevents using a borderline thread (if you need to interact = with >>>>>>> blocking Xenomai services) with SCHED_OTHER and a Linux nice leve= l of 19? >>>>>> Well, this does not really guarantee that the thread will run only= when >>>>>> linux is idle. The thread will eat some cpu time, the nice level i= s not >>>>>> a strict priority, as you know. >>>>> Where do you really need anything stricter? It's the opposite of "I= need >>>>> true 100% CPU for my task, and that forever." >>>>> >>>>>> But in fact, I wonder why Andreas wants >>>>>> a new scheduling policy for xenomai, what is needed, is simply a >>>>>> SCHED_IDLE (maybe it exists ?!) policy for Linux. >>>>>> >>>>> There is no such thing AFAIK. If you are concerned that some CPU >>>>> intensive low prio job eats too much CPU, you normally reduce its >>>>> nice-level and/or confine its CPU bandwidth via cgroups. >>>> SCHED_IDLE exists. >>>> >>> Ah, as "nice 20". Same mechanism, just another level. >>> >> ...and before trying something else: >> >> "SCHED_IDLE: This is even weaker than nice 19, but its not a true >> idle timer scheduler in order to avoid to get into priority >> inversion problems which would deadlock the machine." >=20 > Mmmm, priority inversion? I thought the kernel had priority inheritance= ? >=20 I do not recall the details, but I don't think non-RT priorities are inherited. Moreover, user space locks without explicit inheritance set (ie. the majority of locks) would still cause deadlocks, though not for the kernel. Jan --------------enig6BC71034EF37C0E131FC4D9F 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 iEUEARECAAYFAku1wL0ACgkQitSsb3rl5xTSKgCXVPUWaE4RVyh/BaJmPxI7TCzx nQCePfnQYrrawFEKrXLRDn9mbERMcaY= =nmuN -----END PGP SIGNATURE----- --------------enig6BC71034EF37C0E131FC4D9F--