[Clp] Slow-down on Windows

[Akos Ladanyi]

Hi,

We use CLP in a (pretty large scale) column generation algorithm. On Linux
it works well, however on Windows we experience a peculiar slow-down.
Solving the same problem on Windows takes multiple (!) times longer than on
Linux on the same hardware. Even more strange is that despite solving the
same instance the (wall clock) running time fluctuates heavily on Windows,
while quite stable on Linux.

We tested this both using the COIN-OR-1.7.4-win32-msvc11 prebuilt binaries
from CoinAll, and using our build with Cygwin. It happens with both. We
also tested it on three Windows boxes. We were able to reproduce this on
two. The one where this does not happen is a Windows 7 running in
VirtualBox with a single CPU. The two other, where we get the previously
described behavior, are Windows Server 2008R2 boxes with 4 and 6 CPUs
(cores).

Please let me know if you need any other input to debug this.

Best regards,
Akos Ladanyi
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