Hybrid kernel, not NT

By: Andi Kleen (ak-rwt.delete@this.muc.de), May 9, 2006 2:32 pm
Room: Moderated Discussions

>So in a traditional kernel, you usually would share the
>address space, but you'd have protection issues and some
>semantic differences that mean that the kernel and user
>space can't access each other freely.

> And that makes for
>some really big issues, but a traditional kernel very much
>tries to minimize them. And most importantly, a traditional
>kernel shares the access space across all the basic system
>calls, so that user/kernel difference is the only
>access space boundary.

Traditional unix has the uarea per process which is normally
not accessible by other processes afaik.

iirc some of the BSDs have per process kernel mappings
too. Linux kind of has too with kmap.

>Microkernels are much harder to write and maintain
>exactly because of this issue. You can do simple
>things easily - and in particular, you can do things where
>the information only passes in one direction quite easily,
>but anythign else is much much harder, because there is
>no "shared state" (by design). And in the absense of shared
>state, you have a hell of a lot of problems trying to make
>any decision that spans more than one entity in the

To be fair even in monolithic kernels it is not easy
to share data given races on SMP/preemption etc.
Usually you need to design a locking protocol, care
about livetime issues etc. It's all not simple there

I always admired how elegant some of parallel Erlang programs look and they use message passing
so you certainly can do some stuff cleanly with
messages too.

>And I'm not just saying that. This is a fact. It's a fact
>that has been shown in practice over and over again, not
>just in kernels. But it's been shown in operating systems
>too - and not just once. The whole "microkernels are
>simpler" argument is just bull, and it is clearly shown to
>be bull by the fact that whenever you compare the speed
>of development of a microkernel and a traditional kernel,
>the traditional kernel wins. By a huge amount, too.

How would you describe AmigaOS then? It had a quite
microkernelish structure, but no address space

>The whole argument that microkernels are somehow "more
>secure" or "more stable" is also total crap. The fact that
>each individual piece is simple and secure does not make
>the aggregate either simple or secure. And the
>argument that you can "just reload" a failed service and
>not take the whole system down is equally flawed.

You can rewatch the old movie with Hypervisors and driver domains now @)

There is an old quote from L.Lamport that
fits very well (paraphrased):
"Distributed computing means that you cannot get your
work done when some computer you never heard of crashes"
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TopicPosted ByDate
Hybrid (micro)kernelsTzvetan Mikov2006/05/08 04:41 PM
  Hybrid (micro)kernelsS. Rao2006/05/08 06:14 PM
  Hybrid (micro)kernelsBill Todd2006/05/08 06:16 PM
    Hybrid (micro)kernelsTzvetan Mikov2006/05/08 07:21 PM
      Hybrid (micro)kernelsnick2006/05/08 07:50 PM
      Hybrid (micro)kernelsBill Todd2006/05/09 01:26 AM
        There aren't enough words...Rob Thorpe2006/05/09 02:39 AM
          There aren't enough words...Tzvetan Mikov2006/05/09 03:10 PM
            There aren't enough words...Rob Thorpe2006/05/15 12:25 AM
        Hybrid (micro)kernelsTzvetan Mikov2006/05/09 11:17 AM
          Hybrid (micro)kernelsBill Todd2006/05/09 04:05 PM
  Hybrid (micro)kernelsrwessel2006/05/08 11:23 PM
    Hybrid kernel, not NTRichard Urich2006/05/09 06:03 AM
      Hybrid kernel, not NT_Arthur2006/05/09 07:06 AM
        Hybrid kernel, not NTRob Thorpe2006/05/09 07:40 AM
          Hybrid kernel, not NT_Arthur2006/05/09 08:30 AM
            Hybrid kernel, not NTRob Thorpe2006/05/09 09:07 AM
              Hybrid kernel, not NT_Arthur2006/05/09 09:36 AM
                Linux vs MacOSX peformance, debunked_Arthur2006/05/18 07:30 AM
                  Linux vs MacOSX peformance, debunkedRob Thorpe2006/05/18 08:19 AM
                    Linux vs MacOSX peformance, debunkedAnonymous2006/05/18 12:31 PM
        Hybrid kernel, not NTLinus Torvalds2006/05/09 08:16 AM
          Hybrid kernel, not NTAndi Kleen2006/05/09 02:32 PM
            Hybrid kernel, not NTmyself2006/05/09 03:24 PM
              Hybrid kernel, not NTmyself2006/05/09 03:41 PM
              Hybrid kernel, not NTBrendan2006/05/09 05:26 PM
                Hybrid kernel, not NTLinus Torvalds2006/05/09 08:06 PM
                  Hybrid kernel, not NTBrendan2006/05/13 01:35 AM
                    Hybrid kernel, not NTnick2006/05/13 04:40 AM
                      Hybrid kernel, not NTBrendan2006/05/13 09:48 AM
                        Hybrid kernel, not NTnick2006/05/13 07:41 PM
                          Hybrid kernel, not NTBrendan2006/05/13 09:51 PM
                            Hybrid kernel, not NTnick2006/05/14 05:57 PM
                              Hybrid kernel, not NTBrendan2006/05/14 10:40 PM
                                Hybrid kernel, not NTnick2006/05/14 11:46 PM
                                  Hybrid kernel, not NTBrendan2006/05/15 04:00 AM
                                    Hybrid kernel, not NTrwessel2006/05/15 07:21 AM
                                      Hybrid kernel, not NTBrendan2006/05/15 08:55 AM
                                        Hybrid kernel, not NTLinus Torvalds2006/05/15 09:49 AM
                                          Hybrid kernel, not NTnick2006/05/15 04:41 PM
                                          Hybrid kernel, not NTtony roth2008/01/31 02:20 PM
                                    Hybrid kernel, not NTnick2006/05/15 06:33 PM
                                      Hybrid kernel, not NTBrendan2006/05/16 01:39 AM
                                        Hybrid kernel, not NTnick2006/05/16 02:53 AM
                                          Hybrid kernel, not NTBrendan2006/05/16 05:37 AM
                  Hybrid kernel, not NTAnonymous2008/05/01 10:31 PM
                    Following the structure of the treeMichael S2008/05/02 04:19 AM
                      Following the structure of the treeDean Kent2008/05/02 05:31 AM
                        Following the structure of the treeMichael S2008/05/02 06:02 AM
                        Following the structure of the treeDavid W. Hess2008/05/02 06:48 AM
                          Following the structure of the treeDean Kent2008/05/02 09:14 AM
                            Following the structure of the treeDavid W. Hess2008/05/02 10:05 AM
                              LOL!Dean Kent2008/05/02 10:33 AM
                              Following the structure of the treeanonymous2008/05/02 03:04 PM
                                Following the structure of the treeDean Kent2008/05/02 07:52 PM
                                Following the structure of the treeFoo_2008/05/03 02:01 AM
                                  Following the structure of the treeDavid W. Hess2008/05/03 06:54 AM
                                    Following the structure of the treeDean Kent2008/05/03 10:06 AM
                                      Following the structure of the treeFoo_2008/05/04 01:06 AM
                                        Following the structure of the treeMichael S2008/05/04 01:22 AM
            Hybrid kernel, not NTLinus Torvalds2006/05/09 05:19 PM
              Microkernel Vs Monolithic KernelKernel_Protector2006/05/09 09:41 PM
                Microkernel Vs Monolithic KernelDavid Kanter2006/05/09 10:30 PM
                  Sigh, Stand back, its slashdotting time. (NT)Anonymous2006/05/09 10:44 PM
                  Microkernel Vs Monolithic Kernelblah2006/05/12 08:58 PM
                  Microkernel Vs Monolithic KernelRob Thorpe2006/05/15 01:41 AM
          Hybrid kernel, not NTAnalGuy2006/05/16 03:10 AM
            Theory versus practiceDavid Kanter2006/05/16 12:55 PM
              Distributed algorithmsRob Thorpe2006/05/17 12:53 AM
              Theory versus practiceHoward Chu2006/05/17 02:54 AM
                Theory versus practiceJS2006/05/17 04:29 AM
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  Hybrid (micro)kernelsphilt2006/05/14 09:15 PM
    Hybrid (micro)kernelsLinus Torvalds2006/05/15 08:20 AM
      Hybrid (micro)kernelsLinus Torvalds2006/05/15 11:56 AM
        Hybrid (micro)kernelsRob Thorpe2006/05/16 01:22 AM
          Hybrid (micro)kernelsrwessel2006/05/16 11:23 AM
            Hybrid (micro)kernelsRob Thorpe2006/05/17 12:43 AM
              Hybrid (micro)kernelsrwessel2006/05/17 01:33 AM
                Hybrid (micro)kernelsRob Thorpe2006/05/19 07:51 AM
                  Hybrid (micro)kernelsrwessel2006/05/19 12:27 PM
      Hybrid (micro)kernelstechIperson2006/05/15 01:25 PM
      Hybrid (micro)kernelsmas2006/05/15 05:17 PM
        Hybrid (micro)kernelsLinus Torvalds2006/05/15 05:39 PM
          Hybrid (micro)kernelsColonel Kernel2006/05/15 09:17 PM
            Hybrid (micro)kernelsWink Saville2006/05/15 10:31 PM
              Hybrid (micro)kernelsLinus Torvalds2006/05/16 10:08 AM
                Hybrid (micro)kernelsWink Saville2006/05/16 09:55 PM
          Hybrid (micro)kernelsrwessel2006/05/16 11:31 AM
            Hybrid (micro)kernelsLinus Torvalds2006/05/16 12:00 PM
        Hybrid (micro)kernelsBrendan2006/05/16 01:36 AM
        Hybrid (micro)kernelsPaul Elliott2006/09/03 08:44 AM
          Hybrid (micro)kernelsRob Thorpe2006/09/04 09:25 AM
      Hybrid (micro)kernelsphilt2006/05/16 12:55 AM
        Hybrid (micro)kernelspgerassi2007/08/16 07:41 PM
  Another questionable entry on Wikipedia?Chung Leong2006/05/18 10:33 AM
  Hybrid (micro)kernelsisrael2006/05/20 04:25 AM
    Hybrid (micro)kernelsRob Thorpe2006/05/22 08:35 AM
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