I/O errors seen on programs passing via cygwin under heavy stress

Brebner, Gavin gavin.brebner@hp.com
Thu May 14 10:06:00 GMT 2009

I am routinely having problems with programs compiled and running via cygwin if they are 
using network shares and the level of I/O stress is high. 
In a typical case, I have a single Windows Server 2003 node with a single share open to all, 
and 3 Windows Server 2003 clients each running an up-to-date cygwin who have mounted the share
via a mount //<ip address>/<share> /test. 

On each client I compile and set off the ping_pong locking test which does byte level locking - 
so far so good. If on one of those clients I then set off a heavy load generator compiled and 
running within the cygwin environment e.g. iozone, the ping_pong tests start reporting 
'permission denied' and 'write failed'. iozone itself will generally fail with a write error 
as well.

I have similar issues when using a range of other tests, including when using Samba on Linux 
as the back end server. I have tested with different systems and different networks and seen 
the same result. However, if the load generator is a Windows native application, the 
problem is not seen.

It looks to me as if the cygwin environment has problems if the I/O traffic becomes "excessive".
Note, if the application tries a retry of a failed write after a short delay, it will generally 
succeed, reinforcing my suspicions. 

Googling and looking at the mail archives didn't seem to throw up anything similar, however.
Is this a known issue ? Are there ways of tuning the cygwin I/O subsystem ?



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