process.c: Use getrusage(2) in Process.times

if getrusage(2) is available, to improve precision of Process.times and
its user like lib/benchmark.rb.

On macOS, since getrusage(2) has better precision than times(3),
they are much improved like:

* Before

Process.times
=> #<struct Process::Tms utime=0.56, stime=0.35, cutime=0.04, cstime=0.03>

puts Benchmark.measure { "a" * 1_000_000_000 }
  0.340000   0.310000   0.650000 (  0.674025)

* After

Process.times
=> #<struct Process::Tms utime=0.561899, stime=0.35076, cutime=0.046483, cstime=0.038929>

puts Benchmark.measure { "a" * 1_000_000_000 }
  0.343223   0.310037   0.653260 (  0.674025)

On Linux, since struct rusage from getrusage(2) is used instead of struct tms
from times(2), they are slightly improved like:

* Before

Process.times
=> #<struct Process::Tms utime=0.43, stime=0.11, cutime=0.0, cstime=0.0>

puts Benchmark.measure { "a" * 1_000_000_000 }
  0.120000   0.040000   0.170000 (  0.171621)

* After

Process.times
=> #<struct Process::Tms utime=0.432, stime=0.116, cutime=0.0, cstime=0.0>

puts Benchmark.measure { "a" * 1_000_000_000 }
  0.124000   0.048000   0.172000 (  0.171621)

[ruby-dev:49471] [Feature #11952]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58935 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 4 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 5bfe01b3a0..3f9f620850 100644
--- a/NEWS
+++ b/NEWS
@@ -59,6 +59,10 @@ with all sufficient information, see the ChangeLog file or Redmine
     of #coerce. Return nil in #coerce if the coercion is impossible.
     [Feature #7688]
 
+* Process
+
+  * Precision of Process.times is improved if getrusage(2) exists. [Feature #11952]
+
 * Range
   * Range#initialize no longer rescue exceptions when comparing begin and
     end with #<=> and raise a "bad value for range" ArgumentError