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Date:	Fri, 13 Aug 2010 21:24:02 -0400
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Subject:	Re: Cygwin speed difference on multiple cores -vs- single-core?
From:	mike marchywka <marchywka AT gmail DOT com>
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On 8/13/10, 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?
>
> Thanks much,
>
> andy
>
>

You want to look at details before concluding anything but if it is
real and you blame memory thrashing, I'd be curious to know about it.
This is hardly cygwin specific but people here may be interested.
Usually memory bottleneck kills you first and more processors can just
thrash. At least take a look at task manager and get some idea what
may be going on. Off hand it sounds like it may have more to do with
the file system details based on test you mention. Disk IO and
buffering and syncing can be an issue I would guess.

http://archives.free.net.ph/message/20081115.133519.47f76485.el.html


http://spectrum.ieee.org/computing/hardware/multicore-is-bad-news-for-supercomputers

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