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Reply-To:	Brian DOT Inglis AT SystematicSw DOT ab DOT ca
Subject:	Re: More oddities with multiple processor groups
To:	cygwin AT cygwin DOT com
References:	<87in8xwre7 DOT fsf AT Rainer DOT invalid> <5AD0BAE5 DOT 2040904 AT tlinx DOT org>
From:	Brian Inglis <Brian DOT Inglis AT SystematicSw DOT ab DOT ca>
Message-ID:	<8829ca51-a131-a88b-4b36-00c965af0b2b@SystematicSw.ab.ca>
Date:	Fri, 13 Apr 2018 12:29:31 -0600
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On 2018-04-13 08:12, L A Walsh wrote:
> Achim Gratz wrote:
>> The problem here is that on Linux you don't need to do anything extra to 
>> use any of the advertised logical processors from a single application, 
>> while on Windows you need to first create a thread and set it's affinity to
>> a different group than where your process was started in, then assign each
>> new thread an affinity to one of the available groups.  If you don't do
>> that, all threads will be restricted to the original group.
> Not exactly true.  They are not *restricted* -- it's a *feature* of the
> Windows scheduler, in that future procs/threads inherit the cpu of the
> parent.  Linux's scheduler is more advanced as well as being replaceable.  MS
> doesn't want you to do that
>> there might need to be some option to restrict Cygwin to a single processor
>> group for some applications to work (correctly).
> There is.  Start them all on a single cpu & set the cpu mask.  Pretty much 
> the same way you restrict procs on linux -- you can run them with a specific
> cpu mask, and most programs will keep running w/that mask.
> Unfortunately, AFAIK, I don't think POSIX specifies a way to set affinities,
> so I'm not sure how cygwin would do it.

Glibc adds {pthread,sched}_...affinity... functions.
Linux uses namespaces, control groups (cgroups), cpusets, sysfs/kernfs:
util-linux provides unshare and taskset (not on Cygwin).
BSDs use cpu or processor sets functions and commands.
Mac OS X/Darwin supports either same or different thread cache affinity set and
tag /hints/ (which could be used like cpu sets), but only cache sharing cpu
counts, no explicit cpu identification or control.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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