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Re: autoconf-2.68: test 199 hangs under Cygwin

From: Eric Blake
Subject: Re: autoconf-2.68: test 199 hangs under Cygwin
Date: Mon, 27 Sep 2010 08:02:32 -0600
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On 09/27/2010 12:18 AM, Ralf Corsepius wrote:
3. "make check" is dog-slow on my Cygwin/WinXP system (Each iteration
takes many hours). Part of this slowness certainly originates from the
HW (An N270 Atom netbook), but certainly not all of it (Linux is
reasonably fast on the same machine).

That's also a function of the fact that Cygwin is an emulation layer, and that Windows does not provide native fork() semantics. Linux has copy-on-write process forking, allowing thousands of processes per second, while Cygwin has to manually copy the entire address space with coordination between parent and child process, because Windows does not have any efficient forking mechanism, leading to at most a few hundred fork() per second (and that number goes down the more memory that has to be copied). Any shell script that is fork-intensive, such as the autoconf testsuite, benefits tremendously on Cygwin from any optimization that can reduce the number of forks.

Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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