Project

General

Profile

Feature #11098

Thread-level allocation counting

Added by jasonrclark (Jason Clark) over 5 years ago. Updated about 2 years ago.

Status:
Feedback
Priority:
Normal
Assignee:
-
Target version:
-
[ruby-core:68990]

Description

This patch introduces a thread-local allocation count. Today you can get a
global allocation count from GC.stat, but in multi-threaded contexts that
can give a muddied picture of the allocation behavior of a particular piece of
code.

Usage looks like this:

[2] pry(main)> Thread.new do
[2] pry(main)*   1000.times do
[2] pry(main)*     Object.new
[2] pry(main)*   end
[2] pry(main)*   puts Thread.current.allocated_objects
[2] pry(main)* end
1000

This would be of great interest to folks profiling Ruby code in cases where we
can't turn on more detailed object tracing tools. We currently use GC activity
as a proxy for object allocations, but this would let us be way more precise.

Obviously performance is a big concern. Looking at GET_THREAD, this doesn't
appear to have any clearly large overhead. To check this out, I ran the
following benchmark:

require 'benchmark/ips'

Benchmark.ips do |benchmark|
  benchmark.report "Object.new" do
    Object.new
  end

  benchmark.report "Object.new" do
    Object.new
  end

  benchmark.report "Object.new" do
    Object.new
  end
end

Results from a few run-throughs locally:

Commit 9955bb0 on trunk:

Calculating -------------------------------------
          Object.new   105.244k i/100ms
          Object.new   105.814k i/100ms
          Object.new   106.579k i/100ms
-------------------------------------------------
          Object.new      4.886M (± 4.5%) i/s -     24.417M
          Object.new      4.900M (± 1.9%) i/s -     24.549M
          Object.new      4.835M (± 7.4%) i/s -     23.980M

With this patch:

Calculating -------------------------------------
          Object.new   114.248k i/100ms
          Object.new   114.508k i/100ms
          Object.new   114.472k i/100ms
-------------------------------------------------
          Object.new      4.776M (± 5.1%) i/s -     23.878M
          Object.new      4.767M (± 5.2%) i/s -     23.818M
          Object.new      4.818M (± 1.5%) i/s -     24.154M

I don't have a good sense of whether this is an acceptable level of change or
not, but I figured without writing the code to test there was no way
to know. What do you think?


Files

thread-local.patch (2.04 KB) thread-local.patch jasonrclark (Jason Clark), 04/25/2015 04:19 PM
thread-local-update.patch (2.05 KB) thread-local-update.patch jasonrclark (Jason Clark), 04/27/2016 06:06 PM

Also available in: Atom PDF