I hadn't upgraded my cygwin installation for nine months or so, and when I did, I started having a peculiar performance problem with one of my shell scripts. When you pipe into a "while read xxx; do" loop, it's very slow. I wrote a little benchmark shell script to help me validate this belief, and it's attached.
When I time it with just a bunch of nested "for"
loops, I get the following results:
# time ./doit 1
real 0m2.544s
user 0m0.000s
sys 0m0.000s
When I time it by piping the nested "for" loops into a
"while read" loop, I get the following results:
# time ./doit 2
real 0m22.855s
user 0m0.000s
sys 0m0.000s
As you can see, the "while read" loop seems to have
pitiful performance.
I changed the first line to "#!/bin/bash" to make sure
it wasn't specific to sh as opposed to bash, with the
same results.
I ran the "bash" version of the same benchmark script
on a linux box (basically same version of bash), and
the time doubled between the two passes, which is
pretty much what you would expect, so this seems to be
something in cygwin, not specific to the shell.
Anybody have any idea what's wrong, and how it might
be fixed?
Thanks.
-Russ
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