On Jan 4, 2:23 pm, Case Vanhorsen <cas...@gmail.com> wrote:
> On Mon, Jan 4, 2010 at 1:07 AM, Cactus <rieman...@googlemail.com> wrote:
>
> > On Jan 4, 8:35 am, Cactus <rieman...@googlemail.com> wrote:
> >> 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?
>
> > The memory allocation calls in MPIR are of trhe form
>
> > void *memory(pointer, size_t)
>
> > Since size_t is a 32-bit int on Windows, this will fail if an attempt
> > is made to obtain 2^32 or more _bytes_.
>
> On 64-bit Windows, size_t is __int64. "long" is only 32-bits on x64
> Windows but "long" is 64-bits on 64-bit Linux.
You are right so its not the allocation call itself that is going
wrong
Brian
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