From: pete@...
Date: 2014-08-24T00:23:41+00:00
Subject: [ruby-core:64521] [ruby-trunk - Feature #10165] Use Process.clock_gettime to speed up Benchmark.realtime.

Issue #10165 has been updated by Pete Higgins.

File faster_benchmark_realtime_2.diff added

Eric Wong wrote:
> I like this.  The speedup is from reduction of allocations+GC
>  
>  I think you need to fall back to CLOCK_REALTIME on systems w/o
>  CLOCK_MONOTONIC, though.  Based on my reading of process.c,
>  CLOCK_REALTIME is always available.  So something like this:

It wasn't clear from the docs if there was a way to tell which modes were supported. Thanks for looking into that!

I've made an updated patch with the changes Eric Wong suggested.


----------------------------------------
Feature #10165: Use Process.clock_gettime to speed up Benchmark.realtime.
https://bugs.ruby-lang.org/issues/10165#change-48459

* Author: Pete Higgins
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
----------------------------------------
This patch changes the Benchmark.realtime method to use the Process.clock_gettime internally when generating the time elapsed. Calling Process.clock_gettime is faster than the current way of creating Time objects.

I wrote a benchmark script (also attached) to demonstrate the difference:

```
require 'benchmark'

def old_benchmark
  r0 = Time.now
  yield
  Time.now - r0
end

def new_benchmark
  r0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
  yield
  Process.clock_gettime(Process::CLOCK_MONOTONIC) - r0
end

n = (ARGV.first || 1_000_000).to_i

puts "#{n} iterations."

Benchmark.bmbm do |b|
  b.report("old") { n.times { old_benchmark { nil } } }
  b.report("new") { n.times { new_benchmark { nil } } }
end
```

When I run this on my local machine I see this output:

```
1000000 iterations.
Rehearsal ---------------------------------------
old   0.860000   0.000000   0.860000 (  0.863118)
new   0.360000   0.000000   0.360000 (  0.355242)
------------------------------ total: 1.220000sec

          user     system      total        real
old   0.870000   0.010000   0.880000 (  0.866577)
new   0.330000   0.000000   0.330000 (  0.328982)
```

I discussed this idea originally with Eric Hodel, but he has not reviewed this code.

---Files--------------------------------
benchmark_benchmark_realtime.rb (424 Bytes)
faster_benchmark_realtime.diff (909 Bytes)
faster_benchmark_realtime_2.diff (1.1 KB)


-- 
https://bugs.ruby-lang.org/