Why Ruby 1.9.2 double the speed on 2.53GHz vs 2.2GHz Core 2 Duo?

The following program will take 3.6 seconds to run on a Macbook that has
2.2GHz Core 2 Duo, and 1.8 seconds to run on a Macbook Pro that has
2.53GHz Core 2 Duo.

That’s a bit weird… why doubling the speed when the CPU is only 15%
faster in clock speed? I double checked the CPU meter to make sure none
of the 2 cores are in 100% usage (so as to see the CPU is not busy
running something else). Could it be because one is Mac OS X Leopard
and one is Mac OS X Snow Leopard (64 bit)? Both are running Ruby 1.9.2.


p RUBY_VERSION
p RUBY_DESCRIPTION if defined? RUBY_DESCRIPTION
n = 9_999_999
p n

t = 0; 1.upto(n) {|i| t += i if i%3==0 || i%5==0}; p t


2.2GHz Core 2 Duo

$ time ruby 1.rb
“1.9.2”
“ruby 1.9.2p0 (2010-08-18 revision 29036) [i386-darwin9.8.0]”
9999999
23333331666668

real 0m3.784s
user 0m3.751s
sys 0m0.021s


2.53GHz Intel Core 2 Duo

$ time ruby 1.rb
“1.9.2”
“ruby 1.9.2p0 (2010-08-18 revision 29036) [x86_64-darwin10.4.0]”
9999999
23333331666668

real 0m1.893s
user 0m1.809s
sys 0m0.012s


Test run on Windows 7:

time_start = Time.now

p RUBY_VERSION
p RUBY_DESCRIPTION if defined? RUBY_DESCRIPTION

n = 9_999_999
p n

t = 0; 1.upto(n) {|i| t += i if i%3==0 || i%5==0}; p t

print “Took #{Time.now - time_start} seconds to run\n”


Intel Q6600 Quad Core 2.4GHz running Windows 7, 64-bit

C:> ruby try.rb
“1.9.2”
“ruby 1.9.2p0 (2010-08-18) [i386-mingw32]”
9999999
23333331666668
Took 3.248186 seconds to run


Intel 920 i7 2.67GHz running Windows 7, 64-bit

C:> ruby try.rb
“1.9.2”
“ruby 1.9.2p0 (2010-08-18) [i386-mingw32]”
9999999
23333331666668
Took 2.044117 seconds to run


it is also strange why an i7 with 2.67GHz is slower than a 2.53GHz Core
2 Duo.

winter heat wrote in post #958421:

“ruby 1.9.2p0 (2010-08-18 revision 29036) [i386-darwin9.8.0]”
“ruby 1.9.2p0 (2010-08-18 revision 29036) [x86_64-darwin10.4.0]”

Some of your rubies are built with the old i386 (32 bit) instruction
set, some with the new x86_64 (64 bit) instruction set. The latter is
obviously faster.

64-bit environments are not “obviously” faster than 32-bit. In fact,
some apps run slower when built for 64-bit environment as they end up
moving more stuff in and out of memory, mostly zeros.

However, in this case, the program is dealing with large Integers,
bigger than 31 bits but smaller than 63 bits. On a 32-bit platform they
overflow from a Fixnum to a Bignum. This means that real objects have to
be allocated in memory to represent each value, and they have to be
garbage-collected, whereas on the 64-bit platform they are immediate
values.

Try:

$ ruby -e ‘puts 23333331666668.class’

on both machines.

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