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Re: Serious performance problems (Gerrit/Danny please comment)
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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