cygwin + rsync issue under Windows 7 x64

Wayne Davison wayned at
Sat Mar 6 10:21:24 MST 2010

On Tue, Feb 23, 2010 at 12:55 PM, Eliot Moss <moss at> wrote:
> The latest rsync (3.0.7-1) under an up-to-date cygwin

on Windows 7 x64 gets into some kind of busy wait

situation when transferring large files over ssh.

rsync, ssh, and zip can all be consuming much cpu time.

[...] I downloaded and built rsync 3.0.7 locally, manually
> editing config.status to turn off HAVE_SOCKETPAIR.
> The resulting rsync works fine.

I'd imagine that both ssh and rsync start using a lot of CPU because the
socketpair must be indicating that it is ready for a write (or read) but the
actual write() (or read()) fails to return any bytes (as long as errno is
something like EAGAIN, EINTR, or EWOULDBLOCK, rsync will try again).  If you
want to test that theory, you could add some prints to rsync's io.c file
near the 3 uses of EWOULDBLOCK and have it output what errno it gets.  If
you get that fixed, the programs that interface with a socketpair should go
back to normal.

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