Further to what Jim mentioned below, 64-bit-ness does not imply faster
execution. On the contrary it means each instruction, data address and data
access requires more bits to move across the bus, compared to the 32-bit
version, to do the same work. For example to sort a list of words (text)
the CPU compares byte codes which do not benefit from having 64-bit
registers. But every program variable accessed is done so via a 64-bit
address in stead of a 32-bit address, so this places a bigger load on the
address bus on every operation, without any benefit at all (the data
operated on still fits into 32-bit registers)
If however your application use the features of 64-bit programs then the
advantages can be more than these overheads. For the most part this means
programs that require access to more than 4 GB of data in RAM.
Cheers,
_Johan
On Tue, Aug 17, 2010 at 4:23 AM, Jim Mauro <james.ma...@oracle.com> wrote:
> Typically such performance disparities are due to
> changes in the memory footprint with the 64-bit code,
> and resulting cache miss rates being higher with the
> 64-bit code than the 32-bit code.
>
> You need to use the Studio tools to profile the code,
> and/or cputrack to measure cache hit rates.
>
> Thanks,
> /jim
>
>
> On Aug 16, 2010, at 9:58 PM, 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
> > --
> > This message posted from opensolaris.org
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> > perf-discuss@opensolaris.org
>
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>
--
Any sufficiently advanced technology is indistinguishable from magic.
Arthur C. Clarke
My blog: http://initialprogramload.blogspot.com
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