BASH slow on network share scripts (was RE: A Simple Real World Benchmark for cygwin)

["Dan Vasaru" <dvasaru at broadpark dot no>]

Corinna,

Tnx for taking the trouble of fixing the symlinks. Let's hope it was worth
it :)

I have uncovered another problem now, with the CYGWIN port of bash.
At least when reading/executing a script, bash checks whether the file
descriptor is seekable; if not, it will not perform input buffering of any
kind.

The CYGWIN port of bash short-circuits the test by claiming the input is not
seekable:

bash/input.c
#ifndef __CYGWIN__
#  define fd_is_seekable(fd) (lseek ((fd), 0L, SEEK_CUR) >= 0)
#else
#  define fd_is_seekable(fd) 0
#endif /* __CYGWIN__ */

The result is abysmal performance when the script resides on a network
drive, since bash will read one byte at a time (ultimately resulting in a
network packet per script byte, assuming the OS does not cache the script).

/bin/bash is tens of times slower compared to /bin/sh for an e.g. 200kb
SAMBA-resident script file. I know, it's a BIG script.

Since CYGWIN seems to go to some length to allow O_TEXT seeking, I believe
the ifdef above to be a remnant of some times where cygwin1.dll didn't
support text seeks, and I propose to remove it.

I don't know who to contact on this issue, so someone please notify the
current bash-cygwin maintainer ?

Dan


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