On Sun, May 29, 2005 at 12:32:53AM +0200, Gerrit P. Haase wrote:
>Danny Smith wrote:
>
>>Re: Serious performance problems (Gerrit/Danny please comment)
>>From: Christopher Faylor <cgf-no-personal-reply-please at cygwin dot com>
>>To: cygwin at cygwin dot com
>>Date: Sat, 28 May 2005 14:57:20 -0400
>>Subject: Re: Serious performance problems (Gerrit/Danny please comment)
>>References: <http://sources.redhat.com/ml/cygwin/2005-05/msg01305.html>
>><http://sources.redhat.com/ml/cygwin/2005-05/msg01319.html>
>>Reply-to: cygwin at cygwin dot com
>>
>>--------------------------------------------------------------------------------
>>
>>
>>>On Sat, May 28, 2005 at 01:24:31PM +0200, Vaclav Haisman wrote:
>>>
>>>>Somebody mentioned that malloc implementation could be the problem.
>>>>Dunno. I
>>>>has also crossed my mind that another difference between FreeBSD and
>>>>Cygwin
>>
>>is
>>
>>>>implementation of C++ exceptions. Maybe the SJLJ implementation that
>>>>Cygwin
>>>>AFAIK uses has too big overhead.
>>>
>>>To test this theory, I just tried replacing Cygwin's "Unwind" functions
>>>with those from mingw and saw a noticeable speed up in the execution of
>>>this program. I did this by extracting the contents of mingw's libgcc
>>>to a directory and then including unwind-c.o and unwind-sjlj.o on the
>>>command line when linking the test case. I had to modify the test case
>>>by adding these two lines to the bottom:
>>>
>>> int __mingwthr_key_dtor;
>>> int _CRT_MT;
>>>
>>>to avoid undefined symbol errors so this is obviously not intended as a
>>>complete solution.
>>>
>>>On doing this, the program went from taking 25 seconds to execute to
>>>taking 7 seconds to execute. That's still 4x slower than mingw but it
>>>is, nonetheless, a noticeable difference.
>>>
>>>Gerrit and Danny do you know what the difference between the mingw and
>>>cygwin implementations of these functions might be?
>>>
>>
>>
>>I too suspect sjlj exceptions to be the problem. This has already been
>>reported on GCC lists: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14563
>>
>>The sjlj overhead affects both cygwun and mingw, but cygwin has the
>>additional overhead of posix threads to ensure thread-safe allocation
>>and destruction of structures used by exception handling, while mingw
>>uses win32api directly
>>(In CRT_MT == 0 case, it doesn't even bother cleaning up)
>
>As I thought before, the only difference is buried in w32-shared-ptr.c:
>
>$ g++ -o cygspd-mingw cygspd-mingw.o
>
>$ time ./cygspd-mingw cygspd.dat
>
>real 0m51.071s
>user 0m50.108s
>sys 0m0.046s
>
>cgf, your box must be really fast if this lasts half the time than it
>lasts for me and I have already a really fast box;)
It's pretty fast. This is my famous "hyperthreading machine" running XP
SP2, 3.0GHZ with 1G of memory. I sometimes think that this new machine
tries harder to obscure cygwin bugs than my old machine did.
cygspd runs in 25 - 26 seconds. cygspd-mingw runs in 2 seconds. If I
create dummy versions of
pthread_{getspecific,setspecific,mutex_lock,mutex_unlock}
then the cygwin version is about a second slower than the mingw version.
cgf
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