On Jan 4, 3:26 am, Case Vanhorsen <cas...@gmail.com> wrote:
> On Sun, Jan 3, 2010 at 12:33 PM, Cactus <rieman...@googlemail.com> wrote:
>
> > On Jan 3, 8:15 pm, Case Vanhorsen <cas...@gmail.com> wrote:
> >> Hello,
>
> >> I discovered an interesting memory allocation behavior on Windows vs.
> >> Linux. I was testing GMPY on 64-bit Windows when I stumbled into this.
> >> GMPY replaces the native MPIR memory allocation routines with Python's
> >> memory allocator. If I enable debugging in GMPY, I get a trace of all
> >> the memory allocation calls. When I ran the following:
>
> >> python -mtimeit -n 1 -r 1 -s "import
> >> gmpy;gmpy.mpz(3)**(2**27);gmpy.set_debug(1)" "a=a*a" 2>temp.txt
>
> >> and look at the output saved in temp.txt, I see that Linux generated
> >> approximately 34 memory manager calls but Windows generates over
> >> 100,000 calls. Most of the Windows allocations are for small (<8K)
> >> chunks of memory while all the Linux requests are for more than 64K.
> >> The performance between Linux and Windows is similar. Could it be that
> >> Windows is not using alloca?
>
> >> I also think I found another memory allocation bug. If I run the above
> >> multiplication repeatedly:
>
> >> python -mtimeit -s "import
> >> gmpy;gmpy.mpz(3)**(2**27);gmpy.set_debug(1)" "a=a*a" 2>temp.txt
>
> >> it will eventually crash. In looking at the debug output, I see a
> >> request to allocate 18446744073709498400 bytes of memory.
>
> >> I tested with both MPIR 1.2.2 and 1.3.0 and get similar behavior. I'm
> >> using a custom version of GMPY with some fixes for size_t vs. long
> >> issues that hasn't been committed but I will try to commit those
> >> changes later today.
>
> > Hi Case
>
> > That is _very_ useful information and may explain why Windows
> > performance lgas that on Linux.
>
> > A long time ago - in GMP days - I had to turn of the use of alloca as
> > I kept getting crashes if I used it.
>
> > I have not tried switching it on in MPIR but I will certainly look at
> > this again.
>
> > But _alloca is now deprecated on Windows and its replacement requires
> > a 'free' procedure that alloca doesn't need. It may hence be quite
> > difficult to take advantage of this in future. It all depends on how
> > GMP/MPIR use alloca.
>
> > Thanks for the debugging!
>
> > Brian
>
> Some additional information.
>
> MPIR 1.2.2 generates approximately 172,000 memory allocator calls.
> MPIR 1.3.0 generates approximately 221,000 memory allocator calls.
>
> The count includes both mp_allocate and mp_free.
>
> Performance numbers:
> Windows x64, MPIR 1.2.2: 3.35 seconds
> Windows x64, MPIR 1.3.0, 3.76 seconds
> Linux, MPIR 1.3.0, 3.05 seconds
>
> Processor is a Core2.
>
> Regarding the mp_allocate failure: it looks like it occurs when trying
> to allocate space for a number larger that 2^32 bits long.
Does this allocation failure only occur on Windows?
The MPIR settings for memory management on Windows are:
#define HAVE_ALLOCA 1
#undef HAVE_ALLOCA_H
#undef WANT_TMP_ALLOCA
#undef WANT_TMP_DEBUG
#undef WANT_TMP_NOTREENTRANT
#define WANT_TMP_REENTRANT 1
What are the normal settings used on a Linux/GCC build?
Brian
--
You received this message because you are subscribed to the Google Groups
"mpir-devel" group.
To post to this group, send email to mpir-de...@googlegroups.com.
To unsubscribe from this group, send email to
mpir-devel+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/mpir-devel?hl=en.
