Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756234AbZGNTzV (ORCPT ); Tue, 14 Jul 2009 15:55:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755835AbZGNTzU (ORCPT ); Tue, 14 Jul 2009 15:55:20 -0400 Received: from ms01.sssup.it ([193.205.80.99]:43027 "EHLO sssup.it" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755469AbZGNTzS (ORCPT ); Tue, 14 Jul 2009 15:55:18 -0400 Subject: Re: RFC for a new Scheduling policy/class in the Linux-kernel From: Raistlin To: Peter Zijlstra Cc: "James H. Anderson" , Chris Friesen , Douglas Niehaus , Henrik Austad , LKML , Ingo Molnar , Bill Huey , Linux RT , Fabio Checconi , Thomas Gleixner , Ted Baker , Dhaval Giani , Noah Watkins , KUSP Google Group , Tommaso Cucinotta , Giuseppe Lipari , Bjoern Brandenburg In-Reply-To: <1247589099.7500.191.camel@twins> References: <200907102350.47124.henrik@austad.us> <1247336891.9978.32.camel@laptop> <4A594D2D.3080101@ittc.ku.edu> <1247412708.6704.105.camel@laptop> <1247499843.8107.548.camel@Palantir> <4A5B61DF.8090101@nortel.com> <1247568455.9086.115.camel@Palantir> <4A5C9ABA.9070909@nortel.com> <1247589099.7500.191.camel@twins> Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-Gr5SOStY/8HMQWAPltg5" Date: Tue, 14 Jul 2009 21:54:54 +0200 Message-Id: <1247601294.4839.137.camel@Palantir> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3514 Lines: 91 --=-Gr5SOStY/8HMQWAPltg5 Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Tue, 2009-07-14 at 18:31 +0200, Peter Zijlstra wrote: > > but the discussion since has been entirely about synchronization issues= . >=20 > Right, this seems to be a very hot topic. >=20 Indeed! :-D > Right, Ted holds similar opinions. >=20 > Practically though, active Priority Inheritance has enormous benefits > for us simple people that need to get things done :-) >=20 > It has allowed us to convert this huge mass of code into something that > is real-time enough for a lot of practical uses, including industrial > robots and the like without the need to analyze each and every lock out > there. >=20 As said to you personally, I put quite a lot of efforts trying to find some code using PI-futexes directly or PTHREAD_PRIO_INHERIT POSIX mutexes, for personal curiosity and research interest... But I did not manage for now. :-( Do you think it would be possible to have some pointers? > > In this approach, critical-section lengths must be known, and any > > lock request that occurs when a task doesn't have sufficient > > budget is simply denied -- the request is done later when that task > > receives additional budget. This avoids a task in one group from > > holding a lock while it is preempted (which could severely hurt > > lock-requesting tasks in other groups). This scheme is really easy > > to implement in conjunction with the FMLP and it doesn't require > > complicated budget tracking. Its effects on blocking terms are > > also easy to analyze. Thomas Nolte and colleagues (in Sweden) have > > written some papers where they've used skip-based locks in > > hierarchically-scheduled systems. >=20 > Not granting locks when the contender doesn't have enough budget to > finish them seems like a very attractive solution, however the cost of > having to analyze the critical section seems prohibitive. >=20 I've always thought so... We have some work related to this as well (can give pointers if interested), but I personally like PI/BWI-PEP etc. because such a knowledge is not required at all... Anyway... > That said, we could maybe experiment with this for a few key lock sites. >=20 ... This would be nice! > Furthermore we're limited by the existing legacy (both spec and code > wise), but I think we have been able to make good progress through tools > that help us, such as lockdep and the latency tracer (now ftrace), which > help us find trouble in an active manner. >=20 Well, in my very humble opinion you're definitely doing great job! :-D Regards, Dario --=20 <> (Raistlin Majere) ---------------------------------------------------------------------- Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa (Italy) http://blog.linux.it/raistlin / raistlin@ekiga.net / dario.faggioli@jabber.org --=-Gr5SOStY/8HMQWAPltg5 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEABECAAYFAkpc4o4ACgkQk4XaBE3IOsT7WQCaA43n07lRdElL3mJUuN1fO4D0 f0AAn12dihlRyUy3x/TtCI/SXkTcCz30 =UiOy -----END PGP SIGNATURE----- --=-Gr5SOStY/8HMQWAPltg5-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/