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<H1>Re: [MUD-Dev] Two threads forced to one CPU? (was: Collecting ideas for a MUD server...)</H1>
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<LI><em>To</em>: <<A HREF="mailto:mud-dev#kanga,nu">mud-dev#kanga,nu</A>></LI>
<LI><em>Subject</em>: Re: [MUD-Dev] Two threads forced to one CPU? (was: Collecting ideas for a MUD server...) </LI>
<LI><em>From</em>: "Jay Carlson" <<A HREF="mailto:nop#mitre,org">nop#mitre,org</A>></LI>
<LI><em>Date</em>: Thu, 23 Dec 1999 15:29:41 -0500</LI>
<LI><em>Reply-To</em>: <A HREF="mailto:mud-dev#kanga,nu">mud-dev#kanga,nu</A></LI>
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<PRE>
"J C Lawrence" <claw#kanga,nu> writes:
> On Thu, 23 Dec 1999 01:40:44 -0800 (PST)
> Wesley W Terpstra <terpstra#iota,dhs.org> wrote:
>
> > You're saying if I spawn two threads and having both work nonstop
> > the OS won't put them on different CPUs?
>
> Not necessarily. Further, very few OSes support runtime thread
> migration (IRIX is one of the few FWIW).
[..]
> If you have say a 2-way box with a single process hogging one CPU,
> and the second CPU mostly free, new threads are most likely to be
> assigned to the second CPU. This is reasonable. Now let's say that
> the hoggy process dies, leaving the second CPU hogged with threads
> and the first entirely idle.
>
> Under most current OSes nothing changes. All the threads continue
> execution on the CPU they were originally assigned and the first CPU
> remains idle. Future thread and process starts will likely be
> assigned to the firt CPU, but if there are none it will remain idle.
> Some OSes, and they are very few, will dynamically migrate threads
> between CPUs (and even between nodes in a cluster in some cases (cf
> IRIX CC:NUMA)) at runtime to best use available resources.
I think you need to go reread /usr/src/linux/kernel/sched.c, unless you're
already counting Linux as one of the "very few". Linux is quite willing to
move processes between CPUs in an SMP box. There is a minor bias in favor
of keeping a process assigned to the same CPU, but the current feeling is
that stalling a process to hopefully get a warm cache on its previous CPU is
a waste.
Come to think of it, Solaris 7 on sparc hardware is reassigning processors
for the /usr/local/bin/top process I'm running right now, every fifteen
seconds or so.
Migration between nodes in a cluster, yes, very few operating systems do
that.
Jay
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<LI><STRONG><A NAME="00764" HREF="msg00764.html">[MUD-Dev] Two threads forced to one CPU? (was: Collecting ideas for a MUD server...)</A></STRONG>
<UL><LI><EM>From:</EM> "Wesley W. Terpstra" <terpstra#iota,dhs.org></LI></UL></LI>
<LI><STRONG><A NAME="00771" HREF="msg00771.html">Re: [MUD-Dev] Two threads forced to one CPU? (was: Collecting ideas for a MUD server...)</A></STRONG>
<UL><LI><EM>From:</EM> J C Lawrence <claw#kanga,nu></LI></UL></LI>
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<ul><li>Thread context:
<BLOCKQUOTE><UL>
<LI><STRONG>Re: [MUD-Dev] Collecting ideas for a MUD server... (fwd)</STRONG>, <EM>(continued)</EM>
<ul compact>
<ul compact>
<ul compact>
<ul compact>
<ul compact>
<ul compact>
<ul compact>
<LI><strong><A NAME="00763" HREF="msg00763.html">Re: [MUD-Dev] Collecting ideas for a MUD server... (fwd)</A></strong>,
Rahul Sinha <a href="mailto:rsinha#glue,umd.edu">rsinha#glue,umd.edu</a>, Thu 23 Dec 1999, 17:00 GMT
<UL>
<LI><strong><A NAME="00772" HREF="msg00772.html">Re: [MUD-Dev] Collecting ideas for a MUD server... (fwd)</A></strong>,
J C Lawrence <a href="mailto:claw#kanga,nu">claw#kanga,nu</a>, Thu 23 Dec 1999, 17:48 GMT
</LI>
</UL>
</LI>
</ul>
<LI><strong><A NAME="00764" HREF="msg00764.html">[MUD-Dev] Two threads forced to one CPU? (was: Collecting ideas for a MUD server...)</A></strong>,
Wesley W. Terpstra <a href="mailto:terpstra#iota,dhs.org">terpstra#iota,dhs.org</a>, Thu 23 Dec 1999, 17:00 GMT
<UL>
<LI><strong><A NAME="00771" HREF="msg00771.html">Re: [MUD-Dev] Two threads forced to one CPU? (was: Collecting ideas for a MUD server...)</A></strong>,
J C Lawrence <a href="mailto:claw#kanga,nu">claw#kanga,nu</a>, Thu 23 Dec 1999, 17:31 GMT
<UL>
<LI><strong><A NAME="00776" HREF="msg00776.html">Re: [MUD-Dev] Two threads forced to one CPU? (was: Collecting ideas for a MUD server...)</A></strong>,
Jay Carlson <a href="mailto:nop#mitre,org">nop#mitre,org</a>, Thu 23 Dec 1999, 20:50 GMT
</LI>
<LI><strong><A NAME="00781" HREF="msg00781.html">Re: [MUD-Dev] Two threads forced to one CPU? (was: Collecting ideas for a MUD server...)</A></strong>,
Greg Miller <a href="mailto:gmiller#classic-games,com">gmiller#classic-games,com</a>, Fri 24 Dec 1999, 07:47 GMT
</LI>
</UL>
</LI>
<LI><strong><A NAME="00773" HREF="msg00773.html">Re: [MUD-Dev] Two threads forced to one CPU? (was: Collecting ideas for a MUD server...)</A></strong>,
Marc Bowden <a href="mailto:ryumo#merit,edu">ryumo#merit,edu</a>, Thu 23 Dec 1999, 18:00 GMT
</LI>
</UL>
</LI>
</ul>
</ul>
<LI><strong><A NAME="00749" HREF="msg00749.html">Re: [MUD-Dev] Collecting ideas for a MUD server... (fwd)</A></strong>,
Rahul Sinha <a href="mailto:rsinha#glue,umd.edu">rsinha#glue,umd.edu</a>, Thu 23 Dec 1999, 05:36 GMT
<UL>
<LI><strong><A NAME="00755" HREF="msg00755.html">Re: [MUD-Dev] Collecting ideas for a MUD server... (fwd)</A></strong>,
J C Lawrence <a href="mailto:claw#kanga,nu">claw#kanga,nu</a>, Thu 23 Dec 1999, 06:49 GMT
</LI>
</UL>
</LI>
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