Performance issue

Suleiman Souhlal ssouhlal at
Mon May 9 15:52:42 PDT 2005


On May 9, 2005, at 3:54 PM, Daniel Eischen wrote:

> On Tue, 10 May 2005, Peter Jeremy wrote:
>> On Mon, 2005-May-09 11:00:18 -0400, Ewan Todd wrote:
>>> I have what I think is a serious performance issue with fbsd 5.3
>>> release.  I've read about threading issues, and it seems to me that
>>> that is what I'm looking at, but I'm not confident enough to rule  
>>> out
>>> that it might be a hardware issue, a kernel configuration issue, or
>>> something to do with the python port.
>> There does appear to be a problem in FreeBSD.  Python is built with
>> threading enabled by default, the threading libraries play with the
>> signal mask and there have been extensive changes there.  My
> The threading libraries don't play with the signal mask.  In fact,
> libpthread has userland versions of sigprocmask() et. al. and won't
> even make the syscall() unless the threads are system scope.  There
> is a special thread in libpthread that handles signals which does
> use the system sigprocmask(), but unless the application is
> making heavy use of signals in general, it shouldn't matter.

I think I've found the problem: Python uses setjmp/longjmp to protect  
against SIGFPU every time it does floating point operations. The  
python script does not actually use threads, and libpthread assumes  
non-threaded processes are system scope. So, it would end up using  
the sigprocmask syscall, even though it doesn't really need to.
The diff at 
thr_sigmask-20050509.diff fixes this, by making sure the process is  
threaded, before using the syscall.

Suleiman Souhlal     | ssouhlal at
The FreeBSD Project  | ssouhlal at

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