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Date: Fri, 13 Aug 2010 18:05:40 -0700
From: Tim Prince <n8tm AT aol DOT com>
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Subject: Re: Cygwin speed difference on multiple cores -vs- single-core?
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On 8/13/2010 5:37 PM, Andy Nicholas wrote:
> Hi Folks,
>
> When using cygwin, I've noticed that there seems to be a large speed
> difference when I boot my windows 7 (32-bit) machine in single-core mode
> versus the regular number of cores (4, Core i7-930).
>
> I've read through the FAQ and didn't notice anything about this issue.
>
> Normally, I would expect nearly no speed difference based on the Windows
> environment... but after some extensive timing tests it seems like the single-
> core machine is usually at least 2x faster than using the same machine setup
> in multi-core mode. I limit the number of cores using MSCONFIG, advanced boot
> options.
>
> We have some simple script and more complex scripts which show this behavior.
> The simple scripts do straightforward things like "rm -rf" over some directory
> trees. Even the simple scripts run slowly when the PC is booted with multiple
> cores.
>
> Is this known behavior? Is there some way to work around it so I can boot my
> PC, use all the cores with other apps, and continue run cygwin 2x faster?
>
>    

Several possibilities which you haven't addressed may affect this.
Are you comparing the performance of a single thread when locked to a 
single core, compared to when it is permitted to rotate among cores, 
with or without HyperThread enabled?
I've never run into anyone running win7 32-bit; it may have more such 
issues than the more common 64-bit.

-- 
Tim Prince


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