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From: Achim Gratz <Stromeko AT nexgo DOT de>
To: cygwin AT cygwin DOT com
Subject: Re: More oddities with multiple processor groups
References: <87in8xwre7 DOT fsf AT Rainer DOT invalid>	<b21ad6c9-dadf-6ba2-251a-f374c8fcb89a AT SystematicSw DOT ab DOT ca>
Date: Fri, 13 Apr 2018 21:55:11 +0200
In-Reply-To: <b21ad6c9-dadf-6ba2-251a-f374c8fcb89a@SystematicSw.ab.ca> (Brian	Inglis's message of "Fri, 13 Apr 2018 11:22:29 -0600")
Message-ID: <87lgdq51b4.fsf@Rainer.invalid>
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Brian Inglis writes:
> Have you tried installing and running hwloc package to find out how it sees your
> system?

Yes.  That is OK, but it doesn't change the fact that an application in
Cygwin can see N processors, but then can't actually run on all of them.
If Cygwin would switch the process to processor group aware state by
default then my understanding is that at least the processor group would
have to be explicitly selected for each thread, while on Linux the
scheduler would eventually use all of the NUMA nodes unless the
application tells it prefers different affinities.

> If you run lstopo under X, you get a pretty diagram, but you can also run
> lstopo-no-graphics aka hwloc-ls without X. Running "apropos hwloc" lists
> commands you can use to manipulate the topology.

I'll have that machine switched to "flat mode" which will result in a
single processor group (still with two NUMA nodes, so things like MPI
still know what to do).  I have no actual use for the current topology
and don't want to deal with the obvious complications, especially as I
seem to be the only person who'd have them.  If I can free up some time
I will want to find out why top crashes, but for me that'l be the end of
it if I even get that far.


Regards,
Achim.
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