From: Robert Klemme <shortcutter@...>
Date: 2009-02-25T21:20:52+09:00
Subject: Re: Help interpreting benchmark results

2009/2/25 Sandor Szücs <sandor.szuecs@fu-berlin.de>:
>
> On 24.02.2009, at 23:35, Juan Alvarez wrote:
>
>> These are the results I get:
>>
>>                                 user     system      total        real
>> Curl::Easy.http_get   0.070000   0.130000   0.200000 ( 26.319104)
>> RestClient.get          0.970000   0.580000   1.550000 ( 23.557923)
>>
>> I get these results consistently where curb's user, system and total
>> times are dramatically lower than Net::HTTP's. However, Net:HTTP is
>> reported to run faster by the real column. Shouldn't the reported real
>> time be consistent with the other columns?
>
> No. "real" measures the time that is passed from start to finish.
>
> Pseudocode
>  real_start = Time.now
>  yield # run test
>  real_end = Time.now
>  real_start.to_f - real_end.to_f
>
>
> If the Kernel of your OS schedules another processes for, say 20 seconds,
> then the difference between total and real is >= 20 seconds.
> I think the time called "real" should not be trusted in an evaluation.

Not so fast.  If another process has been running that may well be a
process spawned by our process.

13:19:09 Temp$ ruby19 bb.rb
                          user     system      total        real
other process         0.000000   0.000000   0.139000 ( 10.375000)
in process            4.594000   0.000000   4.594000 (  4.765000)
13:19:30 Temp$ cat bb.rb
require 'benchmark'

Benchmark.bm 20 do |b|
  b.report 'other process' do
    system *%w{sleep 10}
  end

  b.report 'in process' do
    10_000_000.times {|i| i + 1}
  end
end
13:19:35 Temp$

I'd check the curl lib - I would assume that it uses the command line
utility of the same name - which then is another process.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end