l4-hackers August 2005

l4-hackers@os.inf.tu-dresden.de

25 participants
31 discussions

Re: What happens on timeslice overrun?
by Udo A. Steinberg 23 Nov '05

23 Nov '05

On Sun, 14 Aug 2005 22:16:09 +0200 Rene Wittmann (RW) wrote: RW> I have 2 questions on the RT part in DROPS: RW> RW> 1.) I have 2 RT working threads, each with 3 timeslices: RW> Thread 1: period=10ms RW> ts1=30ms prio1=50 RW> ts2=10ms prio2=30 RW> ts3=20ms prio3=50 RW> RW> Thread 2: period=10ms RW> ts1=20ms prio1=40 RW> ts2=5ms prio2=30 RW> ts3=10ms prio3=40 RW> RW> Assume both threads … [View More]are ready at the same time. RW> So thread 1 starts and does its work until it RW> releases the voluntarily or it's preempted by RW> its preempter-thread. So say it releases RW> voluntarily after 20ms. When you say "it's preempted by its preempter thread", do you mean the situation when a preempter with a higher priority than the current thread receives a preemption IPC from the kernel and thus preempts the current thread? RW> Who will get the left 10ms? I guess nobody. When a thread is preempted (that means it gets involuntarily descheduled), the remaining time quantum is saved and later restored when the thread is scheduled again. If the thread yields its scheduling context (that means it voluntarily gives it away), the time quantum is no longer available to the thread. A yield can happen in two ways depending on the target thread id specified: 1) if the target ID is the NIL_ID, then the thread yields its active scheduling context to noone - the time is effectively gone. This is what next_reservation does. Note that the kernel checks the user-specified ID, to guard against the case where a thread wants to yield its active scheduling context and the time quantum on that scheduling context expires simultaneously. 2) if the target ID is a valid thread ID in the system, then the action depends on whether the specified thread is ready to run: a) if it is, then the current thread donates the current scheduling context to the specified thread and that thread then becomes the current thread. This is similar to what happens during a donating IPC. b) if the specified thread is not ready, then the current scheduling context is gone, similar to 1) RW> Or can I assign my left time to a specific RW> thread, say ts2 of thread 1, that is has 20ms RW> after recognizing that ts1 was finished 10ms RW> earlier?I could do with l4_rt_change_timeslice(), RW> but this would probably not work for the the RW> current period! (or yes?) A thread can yield the current scheduling context to another thread as described in 2a) above. Note that the thread will yield the current scheduling context (which may not necessarily be the thread's own active scheduling context). As an example consider: A sends a donating IPC to B, now B runs on A's scheduling context. If B yields to C, then C will run on A's time and B will not donate its own scheduling context. If the current scheduling context is in fact the active scheduling context of the donating thread, then realize that the donating thread will likely encounter a timeslice overrun soon after the yield (the donatee will consume the time quantum until it runs out). If you'd rather avoid that, then the donatee will have to yield the scheduling context back to the owner (the original donator) who then has to yield it to noone. Changes to the time quantum of a scheduling context are only visible the next time that scheduling context becomes the current scheduling context. That means if you change the current scheduling context, then the change will not be visible immediately. RW> 2.) Consider we have a deadline miss. And we say RW> l4_rt_next_period(): would it wait for the beginning RW> of the next (which means: RW> period 1: deadline miss RW> period 2: call next period (because we think we're RW> still in period 1)+ wait to end of period RW> period 3: normal work) RW> Or do I have to care that we do not call RW> l4_rt_next_period() in case of a deadline miss? If your thread misses its deadline right before it wanted to call l4_rt_next_period, then l4_rt_next_period blocks the thread until the end of the new period started due to the deadline miss. Since this is likely not what the thread intended to do, it's the preempter's job to handle that situation, e.g. by ex_regs'ing the thread out of it's l4_rt_next_period call. RW> BTW: I compiled the fiasco-kernel with apic+one shot RW> mode. But this should not be relevant for my question. It is indeed not relevant. -Udo. [View Less]

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RE: Critics on L4 (NOT Re: shared memory Beispiel?)
by yuan Darwin-r62832 02 Sep '05

02 Sep '05

Hi, >Hi L4Ka::Pistachio developers, > >I have read the source code of L4Ka::Pistachio-0.4. & found that some >features defined in L4 eXperimental Kernel Reference Manual Version X.2 Revision 5 hasn't been implemented yet. For example, appoint redirector by SpaceControl, IO port mapping, etc. > > Please understand that both Pistachio and Fiasco are research prototypes and that the L4 eXperimental Kernel Reference Manual is indeed EXPERIMENTAL which means that it may … [View More]change unnoticed and which also means that the prototypes may differ from the specification. The missing features that you state are published, e.g., at http://l4ka.org/projects/pistachio/ia32/ under the section Missing Features / Known Bugs for the Pistachio kernel , respectively at http://os.inf.tu-dresden.de/fiasco/status.html for Fiasco. [Darwin Yuan] Thanks for your information, I started to learn L4 just 1 month. A totally junior. Anything I was wrong, pls correct me. >I tried to checkout the newest source code from CVS, & the CVS server >cvs.l4ka.org couldn't be reached. > > I had no problems reaching the server. Though I cannot confirm that it was up all the time. [Darwin Yuan] Thanks, I'll try later. >When those features are going to be implemented? > Fiasco implements IO Flexpages. Neither Redirectors nor Clans and Chiefs are currently implemented in Fiasco and probably never will. I cannot speak for plans regarding Pistachio. [Darwin Yuan] I didn't read the source code of Fiasco. However, from the documents I got from its website, I found that Clans & Chiefs was implemented in its kernel ( It might be removed now). But I don't think it's a good design that this policy was involved in L4 kernel, now that L4 claims it's a real microkernel. However, I think those kind of policies could be implemented outside kernel. Therefore, I think Redirector is a good mechanism to achieve those kind of policies. That's why I think redirector is very important for implementing a flexible system on L4. >Now that those features are very important for implementing a flexible >OS on L4 u-kernel. > > Both redirectors and IO flexpages are not essential to get a system up and running. Their purpose is to control and restrict communication between threads respectively to prevent a thread from reading / writing IO-ports. Feel free to implement those features if you need them. [Darwin Yuan] Yes, That's true. However, a real system should makes peripheral equipment work. IO Fpage is very essential for implementing hardware driver. Can you elaborate on why you thing missing these features prevents someone building a flexible OS on L4? [Darwin Yuan] As mentioned above. >Seems that there are so many differences between L4Ka::Pistachio and >Fiasco. Is there a stardard L4 specification? > There is a standard L4 Specification: L4-V2 by Jochen Liedtke. Also there is the eXperimental specification you already found which is the defacto standard for L4-V4 kernels. The main difference between Pistachio and Fiasco is that the former implements L4-V4, the latter implements L4-V2 whereby some experimental features have been incorporated into Fiasco to better suite our user level software's needs. As you will see Fiasco already implements some parts of the L4-V4 specification. [Darwin Yuan] I see. Thanks. >I think L4Ka::Pistachio is more clean & flexible, why Fiasco put so >many complicated & inflexible policies inside L4 kernel? > > Which policies are you referring to? Can you elaborate on these points? [Darwin Yuan] For example, Clans & Chiefs. Also, I think "Task" is a redundant abstract/concept, "Address Space" is a much better one. By "Thread" & "Address Space", L4Ka::Pistachio makes the abstract very refined, and allows to construct very flexible system. All together, the APIs of X.2 is much better than X.0. >BTW, has any OS or system been built on L4Ka::Pistachio? As I know, >L4-Linux is built on Fiasco, but I don't like its design. I hope I can >get a reference system based on L4Ka::Pistachio. > > > Lets see, there is L4 Linux which runs on both Fiasco and Pistachio, L4 Env, Drops runs on Fiasco, Kenge, Iguana and Wombat on Pistachio. Also there is Mungi, Perseus, L4 Hurd, etc. Have a look at l4hq.org and you may find out much more. [Darwin Yuan] Thanks for your information. Why don't you like the design of L4Linux or do you mean Fiasco? [Darwin Yuan] Actually, I don't like the APIs & mechanism of Fiasco. Now that L4Linux is based on those APIs & mechanism, I don't like this version of L4Linux. Some more final words: It is common practice on mailing lists to start a new topic if you are referring to a totally different topic. [Darwin Yuan] Honestly, I never use any public mailling list before:(. 'cause this original mail is the first mail I got from this mailing list, I replied it. Someone else has told me about that. Thanks anyway. Best regards Marcus -- Marcus Völp TU-Dresden Department of Computer Science Institute for System Architecture Tel: +49 (351) 463-38350 Fax: +49 (351) 463-38284 [View Less]

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Re: shared memory Beispiel?
by Frank Mehnert 02 Sep '05

02 Sep '05

Hi Mathias, please send questions like this to l4-hackers in every case. Simply because I'm not the only one with knowledge about L4/L4-Userland. The other reason is that other L4 developers might be interested in such questions as well. On Wednesday 31 August 2005 10:03, you wrote: > ich versuche eine L4-Anwendung zu schreiben, die mit shared memory > arbeitet. Konkret soll ein Kernel-Thread in L4Linux-2.6 (ein > Netzwerktreiber-Stub) über den gemeinsamen Speicher mit einem L4-Task … [View More]> (der ausgelagerte Netzwerktreiber) die zu sendenden, bzw. empfangenen > Rahmen austauschen. Ich hab schon im l4/pkg-Verzeichnis nach etwas > passendem gesucht, doch bin nicht wirklich fündig geworden, wie man dass > nun am Besten macht. > Ich will ja nur ein Stück Speicher fester Größe read/write für zwei > L4-Threads mappen. Muss ich dazu den Dataspacemanager benutzen, oder den > Regionmapper, oder gar l4io? Oder geht das vielleicht doch allein mit > den L4.V2-Systemrufen? I would suggest to use the dataspace manager dm_phys to allocate some memory and to map it into both L4Linux 2.6 and the native L4 task. Mapping into the native L4 task should be no problem as long this task has a region manager (the normal case for L4env tasks) -- simply attach the dataspace to the region manager. To map it into L4Linux 2.6, you have to reserve a range of virtual memory inside the Linux server (Adam, which function should someone use for this?) and then map it into that reserved region via l4dm_map_ds() (see dm_phys manual). Since L4Linux 2.6 makes havy use of L4env functionality, this function is available. Make sure that the whole dataspace is mapped into L4Linux since there is no region manager. Finally, make sure that both tasks have the right to map the dataspace. If the Linux server creates the dataspace it has to share the rights explicitly with the native L4 task with l4dm_share(). A more advanced approach would be to use the DSI (DROPS streaming interface) which is also available at the remote CVS. The DSI provides functions for synchronization between clients accessing the same dataspace. There is the dsi_example package. There might be comments from other people reading this list. > Entschuldige, dass ich Dich mit solch banalen Problemen störe, doch ich > weiß eben nicht, wie man das macht und die Dokumentationen (dm_mem, > dm_phys, L4-Referenzmanual, ...) sind dahingehend nicht gerade > aussagekräftig :/ IMHO there still were some threads about this on l4-hackers (please see http://os.inf.tu-dresden.de/mailman/listinfo/) Frank -- ## Dept. of Computer Science, Dresden University of Technology, Germany ## ## http://os.inf.tu-dresden.de/~fm3 ## [View Less]

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RE: shared memory Beispiel?
by yuan Darwin-r62832 31 Aug '05

31 Aug '05

Hi L4Ka::Pistachio developers, I have read the source code of L4Ka::Pistachio-0.4. & found that some features defined in L4 eXperimental Kernel Reference Manual Version X.2 Revision 5 hasn't been implemented yet. For example, appoint redirector by SpaceControl, IO port mapping, etc. I tried to checkout the newest source code from CVS, & the CVS server cvs.l4ka.org couldn't be reached. When those features are going to be implemented? Now that those features are very important for … [View More]

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Re: gcc3.4 problem
by Leon Brits 31 Aug '05

31 Aug '05

Adam, This must be some Ubuntu thing since it compiles fine on a Gentoo box!? Any way now I get "Panic: deceiving ipc"-error after loading the console (l4con) and trying to start "run". Nothing else is loaded (see attachments). Thanks for all your support! Leon

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problem deploying l4env
by Christoph Mueller 25 Aug '05

25 Aug '05

Hello, I tried to build an l4env enabled simple hello world server, but I was not able to deploy it, because the l4env-servers did not start up. (Hello in sigma0-mode did work.) I have attached output from serial console and menu.lst from grub. Thanks, Christoph

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gcc3.4 problem
by Leon Brits 25 Aug '05

25 Aug '05

Hi all, Based on recent posts on this mailing list I decided to also give GCC 3.4 a go and ran into the following error when compiling l4linux-2.4: ljbrits@abc:/home/drops/DROPS/l4linux-2.4 $ make scripts/split-include include/linux/autoconf.h include/config gcc -D__KERNEL__ -I/home/drops/trunk/l4linux-2.4/include -Wall -Wstrict-prototypes -Wno-trigraphs -O2 -fno-strict-aliasing -fno-common -gstabs+ -DLINUX_ON_L4 -I/home/drops/DROPS/l4/include/x86/l4v2 -I/home/drops/DROPS/l4/include/x86 -I/… [View More]

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Interrupt latency in L4Linux
by fabs0028＠free.fr 23 Aug '05

23 Aug '05

Hello, well i 'd like to measure the latency of the interrupts in l4linux, between the moment it is triggered in fiasco and the moment it is aknowledged in the top-halves of linux. Some hints would be greatly appreciated. Thanx for your help. Fabien Chaillou

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Re: l4-hackers Digest, Vol 28, Issue 13
by basant mudalgi 22 Aug '05

22 Aug '05

tanks

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Patches for L4linux
by basant mudalgi 22 Aug '05

22 Aug '05

Hi dont know if this is the right place to send this mail to. I am pretty new to the whole l4 concept. I have been trying to download the l4linux-2.6.12 on my pathetic dial-up connection which is obviously taking longer than expected. i would like to know if there are patches which i can apply to the standard linux (monolithic) kernel to make it an l4linux kernel and save a lot of download time and effort. ie. something like: linux-2.6.xx ----patch----> l4linux-2.6.xx If so where do i find … [View More]

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l4-hackers August 2005