Serious performance problems (Gerrit/Danny please comment)

[Gerrit P. Haase]

Christopher Faylor wrote:

> 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.

Wow, this is really worth to investigate.

> Gerrit and Danny do you know what the difference between the mingw and
> cygwin implementations of these functions might be?

A quick look shows that there are basically no differences in these two 
files, but there a functions called which are defined in
w32-shared-ptr.c, can you include this as well, please?

These parts are Cygwin only:

#ifdef __CYGWIN__
static void __w32_sharedptr_fixup_after_fork (void);
#endif

[...]

#ifdef __CYGWIN__
           /* recreate atom after fork */
           pthread_atfork (NULL,NULL,__w32_sharedptr_fixup_after_fork);
#endif

[...]

#ifdef __CYGWIN__
static void __w32_sharedptr_fixup_after_fork (void)
{
   if (!__w32_sharedptr_set (__w32_sharedptr))
     abort ();
}
#endif


All the rest (in unwind-*) is shared.  So the Cygwin version is slower
for sure.  I don't know why this is needed for Cygwin and not for MinGW,
Danny?


Gerrit
-- 
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