From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751722AbZGaXWN (ORCPT ); Fri, 31 Jul 2009 19:22:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751460AbZGaXWN (ORCPT ); Fri, 31 Jul 2009 19:22:13 -0400 Received: from fg-out-1718.google.com ([72.14.220.152]:15375 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750863AbZGaXWL (ORCPT ); Fri, 31 Jul 2009 19:22:11 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=Gqlg7feVtTeTEwmZ9xmgbbdnt75AtYJ25bNeJDfXUDyeiWVI0Pnd3vLitRZJ0VHR43 qY29Pp8GhilIFY736PHX4+C2Lbqb3JToj8kqH+VlwEYlhPR8Azu1bxZWFR3AmUb3OiEa DIqZCulxktljnBgqp1pS8a41uKuWkHBHlm18o= Date: Sat, 1 Aug 2009 01:22:07 +0200 From: Frederic Weisbecker To: Thomas Gleixner Cc: LKML , rt-users , Ingo Molnar , Steven Rostedt , Peter Zijlstra , Carsten Emde , Clark Williams , Frank Rowand , Robin Gareus , Gregory Haskins , Philippe Reynes , Fernando Lopez-Lezcano , Will Schmidt , Darren Hart , Jan Blunck , Sven-Thorsten Dietrich , Jon Masters Subject: Re: [ANNOUNCE] 2.6.31-rc4-rt1 Message-ID: <20090731232205.GA7574@nowhere> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 30, 2009 at 02:48:04AM +0200, Thomas Gleixner wrote: > We are pleased to announce the next update to our new preempt-rt > series. > > - update to 2.6.31-rc4 > > This is a major rework of the rt patch series. Thanks to Clark > Williams and John Kacur for providing the merge to 2.6.30 while I was > stabilizing .29-rt. While the 30-rt series looked quite stable, we > decided to skip 30-rt entirely to keep track with the ongoing mainline > development for various reaons. The .31-rt series is planned to be > stabilized as we have done with .29-rt. > > The main changes in this release are: > > - interrupt threading > > interrupt threading is now a pure extension of the mainline > threaded interrupt infrastructure. This reduced the patch size of > the forced irq threading to mere > > 8 files changed, 178 insertions(+), 13 deletions(-) > > Another interesting detail is that the new forced threaded code > uses per device threads instead of per interrupt line threads as > we have done in the past. This was just a logical consequence of > the per device thread (voluntary threading) infrastructure in > mainline and allows us now to share an interrupt line between a > hardirq based handler and a threaded handler device. One use case > which comes to my mind is AT91 which shares the timer and the > serial port interrupt; we now can solve that problem w/o nasty > hacks by requesting a threaded handler for the serial port which > shuts up the serial device interrupt in the hard interrupt handler > part. > > - rework of the locking infrastructure > > Up to now the -rt patches changed the raw_spinlock_t to > __raw_spinlock_t and added another two levels of underscores to > many of the locking primitives. A compiler trick was used to chose > the implementation for RT=y and RT=n compiles depending on the lock > type in the lock definition. > > This is nasty as there is no destinction in the source code which > kind of lock we are dealing with except if one looks up the lock > definition/declaration. It definitely was a clever move in the > first place to get things going, but aside of the underscore > conflicts which were introduced by lockdep it was not longer > acceptable to hide the fact that we are treating a lock > differently. Same applies for the changes to (rw_)semaphores which > used the compat_ trick for those ownerless anonymous semaphores > which are taken in one context and released in another. > > The annotation of the code which uses those special treated locks > has been long discussed and one of the proposed solutions was to > change all spinlocks which are converted by -rt to sleeping > spinlocks from spinlock_t to lock_t and have another set of > lock/unlock/trylock functions for those. That is definitely the > _preferred_ solution, but it's a massive and horribly intrusive > change. Steven was working on it for some time, but it simply does > not scale IMNSHO. > > I went the other way round. In -RT we have identified the locks > which can _not_ be converted to sleeping locks and so I went there > and converted them to atomic_spinlock_t and created a set of > functions for them. I converted the already known locks to that > type and fixed up all the functions (s/spin_*/atomic_spin_*/) which > annotates the code and makes it clear what we are dealing with. > > [ I admit "atomic_spinlock_t" is a horrible name, but it's the best > I came up with so far. If you have a better idea please feel free > to add it to > > http://rt.wiki.kernel.org/index.php/Atomic_Spinlock > > instead of starting a bikeshed painting thread on the mailing > lists about that name. Once we have something better it's just a > sed script to fix it. ] > > For !RT the spin_* functions are mapped to atomic_spin_* via inline > functions which do the type conversion. That has another nice side > effect: some places in the kernel (mostly scheduler) use > _raw_spin_* functions on locks to avoid the lockdep invocation in > some places. With the type conversion a lock needs to be defined > atomic_spinlock_t (or raw_spinlock_t) to have access to that > _raw_spin_* functions. Using e.g. _raw_spin_lock() on a lock > defined with spinlock_t/DEFINE_SPINLOCK will cause a compiler > warning. I think that's a Good Thing. > > On RT the spin_* functions are mapped to the corresponding rt_lock > functions with inlines as well. Very simple and much more > understandable than the nifty PICK_OP magic with the underscore > convolution. :) > > I did the same conversion for all (rw_)semaphores which are known > from -rt to be ownerless anonymous semaphores; i.e. taken in one > context and released in another. We renamed them to > compat_(rw_)semaphores up to now and let the compiler pick the > right function. Again here I went down the road and annotated the > code for those with newly created anon_* and [read|write]_anon_* > functions. In !RT the non annotated ones map to the anon_ functions > and on RT we map them to the corresponging rt_* ones. This > annotation should also be helpful to cover at least the non > anonymous (rw_)semaphores via lockdep. > > Part of that semaphore rework is the RFC patch series I posted > recently to get rid of the init_MUTEX[_LOCKED] irritation (minus > the ones which turned out to be wrong) > > The spinlock and semaphore annotation work is separate now and can > be found in the rt/atomic-lock and rt/semaphore branches of the > -tip git repository, which leads me to the next important point: > > - start of gitification > > While reworking all of the above I went through the quilt queue and > sorted out patches into different rt/ branches. If you clone the > -tip git tree you'll find a bunch of branches starting with rt/. > They contain various independent changes which are all part of the > -rt patch. The combination of those branches can be found in the > rt/base branch. > > I still have a leftover of ~140 patches (roughly 40% of the -rt > queue) which I committed into the rt/rt-2.6.31-rc4 branch just as > is simply because I ran out of time. My annual summer vacation > (helping my wife to run the kitchen in the church community kids > summer camp) is starting on friday. > > While the other rt/ branches are mostly bisectable the final one is > not yet there. I restructured the patch queue in a logical way, but > there is more work to be done to clean it up. So expect it to be > replaced. > > Further plans: > > 1) We seriously want to tackle the elimination of the PREEMPT_RT > annoyance #1, aka BKL. The Big Kernel Lock is still used in ~330 > files all across the kernel. A lot of work has been done already to > push down the lock into the code which still thinks it needs to be > protected by it. Some work has been done already in the (a little > bit stale) kill-the-BKL and core/kill-the-BKL branches of the -tip > git tree. If you want to help, please check those branches whether > the code has been tackled already or not to avoid redundant > work. If you decide to take care of one please note it on: > > http://rt.wiki.kernel.org/index.php/Big_Kernel_Lock We (I) can't write to this file :) However, I'll try to attack the remaining bkl that resides in tty... Thanks, Frederic. > > 2) I'm going on vacation for 10 days. Please send patches and > bugreports^Wsuccess stories to the mailinglist as usual. There are > folks looking out. > > Enough said. Get the code and have fun! > > Download locations: > > http://rt.et.redhat.com/download/ > http://www.kernel.org/pub/linux/kernel/projects/rt/ > > Git: > > git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git rt/rt-2.6.31-rc4-rt1 > > Gitweb: > http://git.kernel.org/?p=linux/kernel/git/tip/linux-2.6-tip.git;a=shortlog;h=rt/rt-2.6.31-rc4 > > Information on the RT patch can be found at: > > http://rt.wiki.kernel.org/index.php/Main_Page > > to build the 2.6.31-rc4-rt1 tree, the following patches should be > applied: > > http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.30.tar.bz2 > http://kernel.org/pub/linux/kernel/v2.6/testing/patch-2.6.31-rc4.bz2 > http://www.kernel.org/pub/linux/kernel/projects/rt/patch-2.6.31-rc4-rt1.bz2 > > Thanks to Carsten Emde, Clark Williams and John Kacur who were testing > my various steps to get the code into the shape where it is now. > > Enjoy ! > > tglx > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html