On 8/17/2010 5:09 AM, Rayson Ho wrote:
On Tue, Aug 17, 2010 at 7:59 AM, Johan Hartzenberg<jhart...@gmail.com> wrote:
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.
A lot of applications get a boost in performance in 64-bit because
they get 16 general purpose registers (vs. 8 in 32-bit mode), but this
is true for x64 vs x86 only.
So profile the app and find out where it is spending most time in is
the best starting point.
Exactly.
So when you go from 32-bit to 64-bit code:
- longs and pointers become 64-bits in size. This increases the memory
footprint of the application, and causes the app to become slower.
On x86 you also get:
- An improved ABI where values are passed in registers rather than on
the stack.
- An increased number of registers.
Hence in general x86-64 codes will run faster.
In contrast 32-bit SPARC code uses v8plus which is basically the
advantages of the v9 (64-bit) instruction set with 32-bit pointers and
longs. On SPARC going from 32-bit to 64-bit is nearly always a slight
performance loss due to the increased memory footprint.
As others have said, profile the code to find where the time is spent.
You can profile on the cache miss performance counters. If you're on
Solaris, you can use spot in Studio to generate a report
(http://cooltools.sunsource.net/spot/)
Regards,
Darryl.
Rayson
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
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Compiler Performance Engineering
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