`rb_vm_insns_count` is a global variable used for reporting YJIT
statistics. It is a counter that tallies the number of interpreter
instructions that have been executed, this way we can approximate how
much time we're spending in YJIT compared to the interpreter.
Unfortunately keeping this statistic means that every instruction
executed in the interpreter loop must increment the counter. Normally
this isn't a problem, but in multi-threaded situations (when Ractors are
used), incrementing this counter can become quite costly due to page
caching issues.
Additionally, since there is no locking when incrementing this global,
the count can't really make sense in a multi-threaded environment.
This commit changes `rb_vm_insns_count` to a thread local. That way each
Ractor has it's own copy of the counter and incrementing the counter
becomes quite cheap. Of course this means that in multi-threaded
situations, the value doesn't really make sense (but it didn't make
sense before because of the lack of locking).
The counter is used for YJIT statistics, and since YJIT is basically
disabled when Ractors are in use, I don't think we care about
inaccuracies (for the time being). We can revisit this counter when we
give YJIT multi-threading support, but for the time being this commit
restores multi-threaded performance.
To test this, I used the benchmark in [Bug #20489].
Here is the performance on Ruby 3.2:
```
$ time RUBY_MAX_CPU=12 ./miniruby -v ../test.rb 8 8
ruby 3.2.0 (2022-12-25 revision a528908271) [x86_64-linux]
[0...1, 1...2, 2...3, 3...4, 4...5, 5...6, 6...7, 7...8]
../test.rb:43: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
________________________________________________________
Executed in 2.53 secs fish external
usr time 19.86 secs 370.00 micros 19.86 secs
sys time 0.02 secs 320.00 micros 0.02 secs
```
We can see the regression in performance on the master branch:
```
$ time RUBY_MAX_CPU=12 ./miniruby -v ../test.rb 8 8
ruby 3.5.0dev (2025-01-10T16:22:26Z master 4a2702dafb) +PRISM [x86_64-linux]
[0...1, 1...2, 2...3, 3...4, 4...5, 5...6, 6...7, 7...8]
../test.rb:43: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
________________________________________________________
Executed in 24.87 secs fish external
usr time 195.55 secs 0.00 micros 195.55 secs
sys time 0.00 secs 716.00 micros 0.00 secs
```
Here are the stats after this commit:
```
$ time RUBY_MAX_CPU=12 ./miniruby -v ../test.rb 8 8
ruby 3.5.0dev (2025-01-10T20:37:06Z tl 3ef0432779) +PRISM [x86_64-linux]
[0...1, 1...2, 2...3, 3...4, 4...5, 5...6, 6...7, 7...8]
../test.rb:43: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
________________________________________________________
Executed in 2.46 secs fish external
usr time 19.34 secs 381.00 micros 19.34 secs
sys time 0.01 secs 321.00 micros 0.01 secs
```
[Bug #20489]
Use PR_SET_VMA_ANON_NAME to set human-readable names for anonymous
virtual memory areas mapped by `mmap()` when compiled and run on Linux
5.17 or higher. This makes it convenient for developers to debug mmap.
We used to require MJIT is supported when YJIT is supported. However,
now that RJIT dropped some platforms that YJIT supports, it no longer
makes sense. We should be able to enable only YJIT, and vice versa.
