From: Notmy Realname <guyminuslife@...>
Date: 2010-02-22T06:26:03+09:00
Subject: Re: Read efficiency?

Robert Klemme wrote:
> On 02/21/2010 09:08 AM, Notmy Realname wrote:
>> I hate it when I put my foot in my mouth. After further testing, I'm 
>> almost entirely sure this is just due to overhead, not a problem with 
>> disk access.
> 
> Good that you did not use your real name. ;-)
> 
>> Who would have thought looping 11*2**20 times would incur a performance 
>> hit?
> 
> The overhead of a simple method call is significant already:
> 
> robert@fussel:~$ ruby19 -r benchmark <<XXX
> def f;end # function without effect
> R1=11*1024*1024
> R2=R1/4096
> Benchmark.bmbm 20 do |r|
> r.report("rare") { R2.times { f } }
> r.report("often") { R1.times { f } }
> end
> XXX
> 
> Rehearsal -------------------------------------------------------
> rare                  0.000000   0.000000   0.000000 (  0.000643)
> often                 2.620000   0.000000   2.620000 (  2.663366)
> ---------------------------------------------- total: 2.620000sec
> 
>                            user     system      total        real
> rare                  0.000000   0.000000   0.000000 (  0.000643)
> often                 2.620000   0.000000   2.620000 (  2.665057)
> robert@fussel:~$
> 
> Kind regards
> 
>   robert

I know, right? I'm embarrassed I use this username elsewhere. And I 
spent like an hour trying to figure this out.

In my defense, I did do more or less exactly what you did and found the 
function call overhead to be significant, but not enough to account for 
the difference. Then I remembered that Ruby isn't just doing a disk 
read---it's also doing stuff like packaging the bytes it reads into a 
string. Once I accounted for *that*, the difference magically 
disappeared. Note to self: Ruby is not C.



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