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+[[!meta copyright="Copyright © 2010, 2011, 2013 Free Software Foundation,
+Inc."]]
+
+[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
+id="license" text="Permission is granted to copy, distribute and/or modify this
+document under the terms of the GNU Free Documentation License, Version 1.2 or
+any later version published by the Free Software Foundation; with no Invariant
+Sections, no Front-Cover Texts, and no Back-Cover Texts.  A copy of the license
+is included in the section entitled [[GNU Free Documentation
+License|/fdl]]."]]"""]]
+
+[[!tag open_issue_documentation open_issue_hurd]]
+
+We would expect that fine-grained, compartmentalized systems, that is,
+microkernel-based multi-server systems in particular, would be ideal candidates
+for applying multiprocessing.  That is, however, only true from a first and
+inexperienced point of view: there are many difficulties.
+
+
+# IRC, freenode, #hurd, August / September 2010
+
+    <marcusb> silver_hook: because multi-server systems depend on inter-process
+      communication, and inter-process communication is many times more
+      expensive across cpus
+    <marcusb> silver_hook: so you either force interrelated work on the same
+      cpu, or suffer heavy penalties.  and in a typical fine-grained object
+      system, all objects are interconnected!
+    <marcusb> silver_hook: resources in today's systems, even in a single node
+      with one cpu, but more so in a network, are very non-uniform.  scheduling
+      these resources efficiently is a huge problem.  restricting the resource
+      distribution policies in the way microkernel systems tend to do is posing
+      serious research challenges
+
+
+# IRC, freenode, #hurd, 2011-07-26
+
+    < braunr> 12:03 < CTKArcher> and does the hurd take more advantages in a
+      multicore architecture than linux ?
+    < braunr> CTKArcher: short answer: no
+    < CTKArcher> it's easier to imagine one server pro core than the linux
+      kernel divided to be executed on multiple cores
+    < braunr> CTKArcher: this approach is less efficient
+    < braunr> CTKArcher: threads carry state, both explicit and implicit (like
+      cache data)
+    < braunr> CTKArcher: switching to another core means resetting and
+      refetching this state
+    < braunr> it's expensive and there is no gain obtained by doing this
+    < braunr> thread migration (having a thread from a client also run in
+      servers when making synchronous RPC, even handling its own page faults)
+      was implemented in mach4 and is imo a very good thing we should have
+    < braunr> CTKArcher: and concerning linux, it's actually very scalable
+    < braunr> it's already like if all client threads run in servers (the
+      kernel is the servers there)
+    < braunr> rcu is used a lot
+    < braunr> thread migration already takes into account smt, cores, and numa
+    < braunr> it's hard to do something better
+    < braunr> (here, thread migration means being dispatched on another cpu)
+
+
+# debian-hurd list
+
+On Thu, Jan 02, 2003 at 05:40:00PM -0800, Thomas Bushnell, BSG wrote:
+> Georg Lehner writes:
+>
+> > - One promise of the microkernel architecture is better performance on
+> >   multiprocessor systems, or multicomputer systems. What is the status
+> >   of Gnu Mach with respect to these.
+>
+> This may or may not be true.  The Hurd is built around a microkernel
+> architecture because of its conceptual elegance and flexibility.
+> Other touted advantages may be more illusory than real, at least, they
+> aren't something *we* are proclaiming is our motivation.
+
+
+---
+
+See also: [[multithreading]].