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List:       autoconf-bug
Subject:    Re: autoconf-2.68: test 199 hangs under Cygwin
From:       Eric Blake <eblake () redhat ! com>
Date:       2010-09-27 14:02:32
Message-ID: 4CA0A3F8.60403 () redhat ! com
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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   eblake@redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org


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