[ruby-core:19259] Re: performance of C function calls in 1.8 vs 1.9

On Fri, 10 Oct 2008 13:02:03 +1100, Jason Roelofs <[e-mail]>  
wrote:

> Mike, I think you misunderstand what Paul is pointing out. Compare the
> ration between the Ruby method and C function call times of a test,
> not between 1.8 to 1.9. Using your numbers:
>
>> ruby1.8 test1.rb
>>                          user     system      total        real
>> Ruby method           9.720000   3.150000  12.870000 ( 13.071435)
>> C function            4.800000   0.690000   5.490000 (  5.576923)
>>
>
> C function invocation is about twice as fast than Ruby method invocation
>
>> ruby1.9 test1.rb:
>>                          user     system      total        real
>> Ruby method           2.440000   0.000000   2.440000 (  2.648241)
>> C function            1.880000   0.000000   1.880000 (  1.984703)
>
> C function invocation is about a quarter faster than Ruby method
> evocation, a speed loss of 50%.
>
> Using Paul's initial numbers:
>
> 1.8
>>>                         user     system      total        real
>>> Ruby method           7.170000   0.010000   7.180000 (  7.177720)
>>> C function            3.950000   0.000000   3.950000 (  3.953411)
>
> Again, here it's about twice as fast to call C functions as Ruby methods
>
> 1.9
>>>                         user     system      total        real
>>> Ruby method           8.570000   0.000000   8.570000 (  8.580137)
>>> C function            8.580000   0.000000   8.580000 (  8.591668)
>
> Here it's actually slower to call C functions over Ruby methods.
>
> So the question is: why are C functions now twice as expensive to call
> with 1.9 than with 1.8?

Unless I am completely off-beam here, my understanding of the original  
point (using Paul's numbers) was that the Ruby 1.8 "C function" (3.95 secs  
total) is more than twice as fast as either method under 1.9 (both approx  
8.57 secs). I can understand that this would be a concern. I was simply  
saying that my numbers seem different - mine say that under 1.9 both the  
Ruby method & C function are approximately the same speed, and both are  
slightly faster than the Ruby 1.8 C function. To me those numbers seem  
good.

Are you saying that under 1.9 you would expect the ratio of Ruby method  
time to C function time to remain similar to 1.8 (ie: about 2 to 1)?
With my numbers Ruby 1.9 has certainly sped up the times of the "Ruby  
method", but the "C function" times are similar. I don't understand why  
this should be either disappointing or particularly surprising. Not  
everything in 1.9 is faster than 1.8 - the main thing is that it shouldn't  
be slower.

Cheers
Mike