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diff --git a/open_issues/multiprocessing.mdwn b/open_issues/multiprocessing.mdwn new file mode 100644 index 00000000..562ccd83 --- /dev/null +++ b/open_issues/multiprocessing.mdwn @@ -0,0 +1,82 @@ +[[!meta copyright="Copyright © 2010, 2011 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) + < braunr> some systems like dragonflybsd go as far as to pin threads on one + processor for their entire lifetime + < braunr> in order to have rcu-like locking almost everywhere + < braunr> (you could argue it's less efficient since in the worst case + everything runs on the same cpu, but it's very unlikely, and in practice + most patterns are well balanced) + + +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]]. |