Ruby » Ruby master

mjit.c: introduce JIT compaction [experimental]

When all compilation finishes or the number of JIT-ed code reaches
--jit-max-cache, this compacts all generated code to a single .so file
and re-loads all methods from it.

In the future, it may trigger compaction more frequently and/or limit
the maximum times of compaction to prevent unlimited memory usage.
So the current behavior is experimental, but at least the performance
improvement in this commit won't be removed.

=== Benchmark ===
In this benchmark, I'll compare following four conditions:

• trunk: r64082
• trunk JIT: r64082 w/ --jit
• single-so JIT: This commit w/ --jit
• objfcn JIT: This branch https://github.com/k0kubun/ruby/tree/objfcn w/ --jit,
  which is shinh's objfcn https://github.com/shinh/ruby/tree/objfcn rebased from this commit

$ uname -a
Linux bionic 4.15.0-29-generic #31-Ubuntu SMP Tue Jul 17 15:39:52 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

• Micro benchmark
  Using this script https://gist.github.com/k0kubun/10e6d3387c9ab1b134622b2c9d76ef51,
  calls some amount of different methods that just return nil. The following tables
  are its average duration seconds of 3 measurements.

Smaller is better.

** 1 method (seconds)

** 50 methods (seconds)

** 1500 methods (seconds)

• Discourse
  Using the same benchmark strategy as https://bugs.ruby-lang.org/issues/14490 with
  this branch https://github.com/k0kubun/discourse/commits/benchmark2 forked from discourse
  v1.8.11 to support running trunk.

1. Run ruby script/bench.rb to warm up profiling database
2. Run RUBYOPT='--jit-verbose=1 --jit-max-cache=10000' RAILS_ENV=profile bin/puma -e production
3. WAIT 5-15 or so minutes for all jitting to stop so we have no cross talk
4. Run ab -n 100 http://localhost:9292/
5. Wait for all new jitting to finish
6. Run ab -n 100 http://localhost:9292/

** Response time (ms)
Here is the response time milliseconds for each percentile.
Skipping 99%ile because it's the same as 100%ile in 100 calls.

| | trunk| trunk|single|objfcn|

** Ratio (smaller is better)
Here is the response time increase ratio against no-JIT trunk's one.

| | trunk| trunk|single|objfcn|

While 50 and 60 %ile are still worse than no-JIT trunk, 75, 80, 90, 95,
98 and 100% are not slower than that.

So now it's a little harder to say "MJIT slows down Rails applications".
Probably I can close [Bug #14490] now. Let's start improving it.

Close https://github.com/ruby/ruby/pull/1921

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64094 b2dd03c8-39d4-4d8f-98ff-823fe69b080e