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Date: Wed, 5 May 2010 07:18:46 -0400
Message-ID: <z2pb0ddfae81005050418h2a341f41hcc92e3110c6cc6e2@mail.gmail.com>
Subject: Re: cpu usage capped?
From: mike marchywka <marchywka AT gmail DOT com>
To: cygwin AT cygwin DOT com
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On 5/5/10, Mark Geisert <mark AT maxrnd DOT com> wrote:
>> I have some code that takes advantage of 8 cores on my machine using
>> OpenMP. Under plain ol windows, this code causes all the CPUs to max

on some computers you can get things like virus protection software to
do thta. LOL. My point of course, inline with comments below, is that
CPU usage doesn't equate to getting anything useful done. This could
be time spent doing thread-threed communications, who knows.

>> out at 99%. But when recompiled for cygwin, each core jumps to about
>> 85%. The rest is not being used by other processes. Could someone
>> explain why this is the case?

Usually this is VM or IO or maybe lock starvation. In all seriousness, this
could occur if the compiled code is significantly better
although last time I looked years ago the MS compilers were supposed
to be better, and INTC compiler the best  but it depends on options
etc.  You need to do a wall clock performance test here. Also these
things can be quite sensitive to specific conditions, your mileage
may vary.

>
> Obviously, Cygwin gets the job done with less CPU utilization, handing you
> back
> 15% of your machine.  And you're complaining?
>
> ..mark
>
> P.S. A more helpful response can likely only occur if you spell out more
> specifically which varieties of apples and oranges you're comparing.  For
> starters: "plain ol windows", is that MSVC or MinGW?  Is disk I/O involved?
> What OS and environment (e.g., VM? TS?).  I'm pretty sure I'm only
> scratching
> the surface here.  We don't know what your code does other than use OpenMP.
>
>
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