[CentOS] Is 4GB memory the 64bit switch tipping point?

NiftyClusters T Mitchell niftycluster at niftyegg.com
Fri Dec 12 07:17:14 UTC 2008


On Sun, Dec 7, 2008 at 10:06 PM, Kenneth Burgener
<kenneth at mail1.ttak.org> wrote:
> I am curious what should be the benchmark for making the choice of
> switching from 32bit to 64bit Linux?  I have a few assumptions below.
> Is my logic sound?  (This is a follow up to the "Adding RAM" thread)
>
> Assumptions:
>
> 1.  4GB Memory.  The main benefit of 64bit mode is the ability to
> address more than 4GB of RAM.
......
Lots of other good responses but the critical
tipping point after functionality is 'benchmark results' as noted in
the opening paragraph.  The next is data set size but with a little
care in the code this is mostly not an issue (size of pipe is BIG)
so as long as the kernel can address and manage all memory it
is the rare application+data set that needs 64bit longs and pointers.

The point about benchmarking is critical when deciding 64bit .vs. 32 bit.
Modern x86_64 processors can run both 32bit and 64bit applications, the
key is that the processor register and instruction set is richer in
64bit mode which permits the compiler to do more for many but not all
applications.

The ability of compilers to take advantage of the richer 64bit ABI can be
massive.  I have seen Fortran and C programs improve as much as +70%

The gcc family of compilers is much improved over gcc of 5 years ago.
Specialty vendor compilers can still show important gains over gcc so kick the
tires when ya can.

YMMV.

Later,
mitch



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