It can be as simple as impact on the cache. 64-bit programs tend to be
bigger, and so they have a worse effect on the i-cache.
Unless your program does something that can inherently benefit from
64-bit registers, or can take advantage of the richer instruction set
that is available to amd64 programs, you probably will see a degradation
when running 64-bit programs.
That said, I think a great number of programs *do* benefit from the
larger registers, and from the richer ISA available to 64-bit programs.
- Garrett
On Mon, 2010-08-16 at 18:58 -0700, Kishore Kumar Pusukuri wrote:
> Hi,
> I am surprised with the performances of some 64-bit multi-threaded
> applications on my AMD Opteron machine. For most of the applications, the
> performance of 32-bit version is almost same as the performance of 64-bit
> version. However, for a couple of applications, 32-bit versions provide
> better performance (running-time is around 76 secs) than 64-bit (running time
> is around 96 secs). Could anyone help me to find the reason behind this,
> please?
>
>
> $ldd program-64 (64-bit version)
> libpthread.so.1 => /lib/64/libpthread.so.1
> libstdc++.so.6 => /usr/lib/64/libstdc++.so.6
> libm.so.2 => /lib/64/libm.so.2
> libgcc_s.so.1 => /usr/lib/64/libgcc_s.so.1
> libc.so.1 => /lib/64/libc.so.1
>
> $ ldd program-32 (32-bit version)
> libpthread.so.1 => /lib/libpthread.so.1
> libstdc++.so.6 => /usr/lib/libstdc++.so.6
> libm.so.2 => /lib/libm.so.2
> libgcc_s.so.1 => /usr/lib/libgcc_s.so.1
> libc.so.1 => /lib/libc.so.1
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