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[[!tag open_issue_gnumach]]

<http://www.brynosaurus.com/pub/os/thread-migrate.pdf>

  * [[microkernel/mach/memory_object/discussion]]

  * [[resource_management_problems]]


# IRC, freenode, #hurd, 2013-08-13

In context of [[resource_management_problems]].

    <braunr> and thread migration itself is something very confusing
    <braunr> it's better to think of it as scheduling context inheritance
    <teythoon> braunr: I read the paper I mentioned and then I wanted to find
      the sources they modified
    <teythoon> I failed
    <teythoon> I hate scientific paper about software that fail to provide the
      source code
    <teythoon> that's not science imho b/c it's not reproducible
    <braunr> i have some osf source code here
    <braunr> i'll send it if you want
    <teythoon> ah interesting
    <braunr> but really, when you dive into it, thread migration is merely
      scheduling context inheritance with kernel upcalls
    <braunr> it's good
    <teythoon> I searched for osf mach but google didn't turned up anything
    <braunr> but it has nothing to do with resource accounting
    <braunr> (well, it may hepl better account for cpu time actually)
    <braunr> help*
    <braunr> but that's all
    <teythoon> why is that all? wouldn't that be transitive and could also be
      used for i/o accounting?
    <teythoon> also I tried to find alternative mach implementations
    <teythoon> I wasn't terribly successful, and some sites are gone or
      unmaintained for years :/
    <braunr> we don't need that for io accountin
    <braunr> g
    <braunr> thread migration is a kernel property
    <braunr> on mach with userspace drivers, io isn't
    <braunr> mach should only control cpu and memory
    <braunr> and you though you can account physical memory, you can't transfer
      virtual memory accounting from one task to another
    <teythoon> yes, but once all of those resources can be accounted to the
      thread initiating whatever it needs doing, shouldn't that be much easier?
    <braunr> teythoon: it's not required for that
    <braunr> teythoon: keep in mind userspace sees activations
    <braunr> in a thread migration enabled kernel, activations are what we
      usually call threads, and threads are scheduling contexts
    <teythoon> braunr: ok, so TM is not required for accounting, but surely
      it's a good thing to have, no?
    <braunr> teythoon: it's required for cpu accounting only
    <braunr> which is very important :)
    <braunr> if you look carefully, you'll see hurd servers are what use most
      cpu
    <braunr> there is now easy way to know which application actually uses the
      server
    <braunr> i personally tend to think more and more that servers *should*
      impersonate clients
    <braunr> TM (or rather, scheduling context inheritance) is one step
    <braunr> it's not enough exactly because it doesn't help with resource
      accounting
    <braunr> teythoon:
      ftp://ftp.mklinux.org/pub/mklinux-pre-R1/SRPMS/sources/osfmk.tar.gz


# IRC, freenode, #hurd, 2013-09-02

[[!taglink open_issue_documentation]]: move information to
[[microkernel/mach/history]].

    <teythoon> braunr: btw, I just noticed lot's of #ifdef MIGRATING_THREADS in
      gnumach, so there was some work being done in that direction?
    <braunr> gnumach is a fork of mach4
    <braunr> at a stage whre migration was being worked on, yes
    <teythoon> from what I've gathered, gnumach is the only surviving mach4
      fork, right?
    <braunr> yes
    <braunr> well
    <braunr> the macos x version is probably one too
    <braunr> i don't know
    <teythoon> oh? I read that it was based on mach3
    <braunr> it is
    <braunr> i can't tell how much of mach3 versus mach4 it has, and if it's
      relevant at all
    <teythoon> and the osfmach, was that also based on mach4?
    <braunr> yes
    <teythoon> ok, fair enough
    <braunr> that's why i think macos x is based on it too
    <braunr> i initially downloaded osfmach sources to see an example of how
      thread migration was used from userspace
    <braunr> and they do have a special threading library for that