From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <51767CF9.5090808@siemens.com> Date: Tue, 23 Apr 2013 14:22:17 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <201304191346.38739.leo@alaxarxa.net> <517195B6.8020209@xenomai.org> <12ABCC03-FADF-4C5A-9CAE-CD9E5CA63A19@mah.priv.at> <51724F82.2000809@web.de> <5172B0E5.7090806@xenomai.org> <5172B1B5.10804@web.de> <5172B28C.6070503@xenomai.org> <5172B3CD.20007@web.de> <5172B4AA.1060704@xenomai.org> <5174E2A0.1040906@siemens.com> <51752114.7040903@xenomai.org> <51753E59.4090609@siemens.com> <51758816.4050100@xenomai.org> <51764485.9020403@siemens.com> <51766E65.1010304@xenomai.org> In-Reply-To: <51766E65.1010304@xenomai.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai] Default options in the debian package List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: "xenomai@xenomai.org" On 2013-04-23 13:20, Gilles Chanteperdrix wrote: > On 04/23/2013 10:21 AM, Jan Kiszka wrote: > >> On 2013-04-22 20:57, Gilles Chanteperdrix wrote: >>> On 04/22/2013 03:42 PM, Jan Kiszka wrote: >>> >>>> On 2013-04-22 13:37, Gilles Chanteperdrix wrote: >>>>> On 04/22/2013 09:11 AM, Jan Kiszka wrote: >>>>> >>>>>> On 2013-04-20 17:30, Gilles Chanteperdrix wrote: >>>>>>> On 04/20/2013 05:27 PM, Jan Kiszka wrote: >>>>>>> >>>>>>>> On 2013-04-20 17:21, Gilles Chanteperdrix wrote: >>>>>>>>> On 04/20/2013 05:18 PM, Jan Kiszka wrote: >>>>>>>>> >>>>>>>>>> On 2013-04-20 17:14, Gilles Chanteperdrix wrote: >>>>>>>>>>> On 04/20/2013 10:19 AM, Jan Kiszka wrote: >>>>>>>>>>> >>>>>>>>>>>> On 2013-04-20 08:04, Michael Haberler wrote: >>>>>>>>>>>>> >>>>>>>>>>>>> Am 19.04.2013 um 21:06 schrieb Gilles Chanteperdrix : >>>>>>>>>>>>> >>>>>>>>>>>>>> On 04/19/2013 01:46 PM, Leopold Palomo-Avellaneda wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>> [1] >>>>>>>>>>>>>>> http://lists.mech.kuleuven.be/pipermail/orocos-users/2013-April/006986.html >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> Hi, >>>>>>>>>>>>>> >>>>>>>>>>>>>> that link does not tell us why you need this option. And that would be >>>>>>>>>>>>>> the most important information. >>>>>>>>>>>>> >>>>>>>>>>>>> with the linuxcnc package build I need to turn on --enable-dlopen-skins as well to get Python modules to work properly >>>>>>>>>>>> >>>>>>>>>>>> OK, it looks like we should try harder to detect dlopen scenarios during >>>>>>>>>>>> runtime to avoid build-time switches. This is likely Xenomai 3 material: >>>>>>>>>>>> >>>>>>>>>>>> - We need to disable TLS optimizations by default (no big deal). >>>>>>>>>>>> >>>>>>>>>>>> - In the POSIX skin constructor, we need to read out the mlockall >>>>>>>>>>>> state, lock everything if necessary, and restore the state >>>>>>>>>>>> accordingly afterward. The Nucleus may help us here if there is no >>>>>>>>>>>> adequate libc service (ABI change -> Xenomai 3). >>>>>>>>>>>> >>>>>>>>>>>> - IIRC, the problem with unconditional auto-shadowing back then were >>>>>>>>>>>> the improper scheduling parameters that POSIX used to apply. That >>>>>>>>>>>> was fixed a while back. So if we simple re-apply the current >>>>>>>>>>>> parameters, it should cause no harm in a dlopen scenario. But I need >>>>>>>>>>>> to check this again at work against our scenario. >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> You do not like the idea of an environment variable allowing to disable >>>>>>>>>>> the automatic shadowing? >>>>>>>>>> >>>>>>>>>> Not as a long-term solution as it is user-unfriendly. But it can be an >>>>>>>>>> option worth considering for 2.6. >>>>>>>>> >>>>>>>>> >>>>>>>>> Apparently -forge is already doing it. The advantage of this solution is >>>>>>>>> that the same binary serves well several usages, if we intend to provide >>>>>>>>> packages as generic as possible, this seems like the way to go. Several >>>>>>>>> of the changes I made in the last few weeks go in the same direction. >>>>>>>> >>>>>>>> I'm not sure if there is added value for the controlling auto-shadowing >>>>>>>> in general. But for the case it is in conflict with dlopen, the solution >>>>>>>> I'm proposing is clearly superior as it removes those conflicts >>>>>>>> automatically. >>>>>>>> >>>>>>>> Of course, an environment variable control can exist in parallel if >>>>>>>> there is a need beyond the dlopen conflict resolution. >>>>>>> >>>>>>> >>>>>>> The difference with what you propose is that you propose a syscall to >>>>>>> get the mlockall state. Another solution would be not to call munlockall >>>>>>> after the main thread shadowing, this looks less complicated and does >>>>>>> not require ABI changes. >>>>>> >>>>>> Yes, that's an option as well. But then we should apply this >>>>>> consistently, invoking mlockall from all skin init functions >>>>>> unconditionally. The nucleus depends on this anyway. Not sure if such >>>>>> change would be fine for 2.6 - you decide. >>>>> >>>>> >>>>> What we could do is: >>>>> - if XENO_NOSHADOW is set, shadow the main thread, and call mlockall >>>>> - if it is not set, do not shadow the main thread or call >>>>> mlockall/munlockall >>>> >>>> That's not what I suggested. I was questioning the value of _not_ doing >>>> mlockall automatically during init, thus reducing user duties. That >>>> would reduce the need to think about XENO_NOSHADOW or not as a normal user. >>> >>> >>> Currently, when the posix skin library start, it does: >>> mlockall >>> shadow main thread >>> munlockall >>> >>> Now, the munlockall is certainly an issue when dlopening >>> >>> What I propose instead is to do: >>> if (!getenv("XENO_NOSHADOW")) { >>> mlockall >>> shadow main thread >>> } >>> >>> That will avoid the problem with calling munlockall, and if people who >>> currently use --enable-dlopen-skins really want to avoid shadowing the >>> main thread (which I doubt), they can set the environment variable >>> XENO_NOSHADOW. >> >> Totally clear. But why still requiring the application to call mlockall >> if we do not autoshadow or use a different skin? It's pointless to have >> this explicit call in the application if we can easily do this from the >> library. > > > Well, we have --enable-posix-auto-mlockall for that. But you are right, > we get rid of all this and enable automatic mlockall for all skins. I do > not see any drawbacks. Perfect. Will work out some patches. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SDP-DE Corporate Competence Center Embedded Linux