Cygwin slow on x64 systems
Mon Aug 30 11:23:00 GMT 2010
For the last couple of weeks I'm trying to identify the cause for cygwin
slowdown on x64 machines which was reported by David Morgan about 6
I wrote a little bash script which prints the result of 'date -s' to a
file in a loop and then counts the number of times the same second
appears in that file.
I used this script to test all available cygwin revisions snapshots
(which I downloaded from
ftp://www.fruitbat.org/pub/cygwin/circa/index.html) for cygwin version
I was able to identify the exact change which introduce the slowdown.
With my test script for cygwin version 1.5.19-4, snapshot timestamp
1142005204 I'm able to get ~40 lines/second, but with the same version,
snapshot timestamp 1142338816 the result is ~18 lines/second.
Using cvsps I was able to generate a patchset which contains all the
changes between those 2 revisions.
I then applied the changes one by one and built cygwin1.dll for each
change, then I ran my test script again for each cygwin1.dll version and
I found that the change to winsup/cygwin/dcrt0.cc from '2006/03/12
23:57:03' introduce this issue.
The log for this change is :
* dcrt0.cc (dll_crt0_0): Call sigproc_init during init startup.
(_dll_crt0): Don't worry about sync_startup. Just wait for sigthread here.
This change includes 2 different sub-changes :
1. Moving the call to sigproc_init from dll_crt0_1 function to
dll_crt0_0 - which doesn't affect performance.
2. a. Moving the call to wait_for_sigthread from dll_crt0_1 to _dll_crt0
which calls dll_crt0_1.
b. Deleting the call to WaitForSingleObject,
i.e. : "Don't worry about sync_startup"
I can confirm that the 2nd sub-change is the cause for the slowdown.
Any help will be appreciated.
Sagi Ben-Akiva - sagi at graphtech dot co dot il
GraphTech Computer Systems
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