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Re: Cygwin speed difference on multiple cores -vs- single-core?


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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