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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
# IRC, freenode, #hurd, 2014-02-18
<teythoon> has anyone here ever tried to enable the thread migration bits
in gnumach to see where things break and how far that effort has been
taken ?
<braunr> without proper userspace support, i don't see how this could work
<teythoon> but is the kernel part finished or close to being finished ?
<braunr> no idea
<braunr> i don't think it is
<braunr> i didn't see much code related to that feature, and practically
none that looked like what the paper described
<braunr> some structures, but not used
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