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YJIT: add MPLR talk link. Encourage users to use --yjit-mem-size (#12305)

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* Add MPLR talk. Encourage users to use --yjit-mem-size.

* Improve text
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@ -19,6 +19,7 @@ This project is open source and falls under the same license as CRuby.
If you wish to learn more about the approach taken, here are some conference talks and publications: If you wish to learn more about the approach taken, here are some conference talks and publications:
- MPLR 2023 talk: [Evaluating YJIT’s Performance in a Production Context: A Pragmatic Approach](https://www.youtube.com/watch?v=pVRmPZcNUhc)
- RubyKaigi 2023 keynote: [Optimizing YJIT’s Performance, from Inception to Production](https://www.youtube.com/watch?v=X0JRhh8w_4I) - RubyKaigi 2023 keynote: [Optimizing YJIT’s Performance, from Inception to Production](https://www.youtube.com/watch?v=X0JRhh8w_4I)
- RubyKaigi 2023 keynote: [Fitting Rust YJIT into CRuby](https://www.youtube.com/watch?v=GI7vvAgP_Qs) - RubyKaigi 2023 keynote: [Fitting Rust YJIT into CRuby](https://www.youtube.com/watch?v=GI7vvAgP_Qs)
- RubyKaigi 2022 keynote: [Stories from developing YJIT](https://www.youtube.com/watch?v=EMchdR9C8XM) - RubyKaigi 2022 keynote: [Stories from developing YJIT](https://www.youtube.com/watch?v=EMchdR9C8XM)
@ -228,15 +229,18 @@ they might not necessarily be the best configuration for your application.
This section covers tips on improving YJIT performance in case YJIT does not This section covers tips on improving YJIT performance in case YJIT does not
speed up your application in production. speed up your application in production.
### Increasing --yjit-exec-mem-size ### Increasing --yjit-mem-size
When JIT code size (`RubyVM::YJIT.runtime_stats[:code_region_size]`) reaches this value, The `--yjit-mem-size` value can be used to set the maximum amount of memory that YJIT
YJIT stops compiling new code. Increasing the executable memory size means more code is allowed to use. This corresponds to the total of `RubyVM::YJIT.runtime_stats[:code_region_size]`
and `RubyVM::YJIT.runtime_stats[:yjit_alloc_size]`
Increasing the `--yjit-mem-size` value means more code
can be optimized by YJIT, at the cost of more memory usage. can be optimized by YJIT, at the cost of more memory usage.
If you start Ruby with `--yjit-stats`, e.g. using an environment variable `RUBYOPT=--yjit-stats`, If you start Ruby with `--yjit-stats`, e.g. using an environment variable `RUBYOPT=--yjit-stats`,
`RubyVM::YJIT.runtime_stats[:ratio_in_yjit]` shows the ratio of YJIT-executed instructions in %. `RubyVM::YJIT.runtime_stats[:ratio_in_yjit]` shows the percentage of total YARV instructions
Ideally, `ratio_in_yjit` should be as large as 99%, and increasing `--yjit-exec-mem-size` often executed by YJIT as opposed to the CRuby interpreter.
Ideally, `ratio_in_yjit` should be as large as 99%, and increasing `--yjit-mem-size` often
helps improving `ratio_in_yjit`. helps improving `ratio_in_yjit`.
### Running workers as long as possible ### Running workers as long as possible
@ -254,16 +258,13 @@ you may want to reduce the killing frequency or increase the limit.
YJIT allocates memory for JIT code and metadata. Enabling YJIT generally results in more memory usage. YJIT allocates memory for JIT code and metadata. Enabling YJIT generally results in more memory usage.
This section goes over tips on minimizing YJIT memory usage in case it uses more than your capacity. This section goes over tips on minimizing YJIT memory usage in case it uses more than your capacity.
### Decreasing --yjit-exec-mem-size ### Decreasing --yjit-mem-size
The `--yjit-exec-mem-size` option specifies the JIT code size, but YJIT also uses memory for its metadata, YJIT uses memory for compiled code and metadata. You can change the maximum amount of memory
which often consumes more memory than JIT code. Generally, YJIT adds memory overhead by roughly that YJIT can use by specifying a different `--yjit-mem-size` command-line option. The default value
3-4x of `--yjit-exec-mem-size` in production as of Ruby 3.3. You should multiply that by the number is currently `128`.
of worker processes to estimate the worst case memory overhead. When changing this value, you may want to monitor `RubyVM::YJIT.runtime_stats[:ratio_in_yjit]`
as explained above.
`--yjit-exec-mem-size=48` is the default since Ruby 3.3.1,
but smaller values like 32 MiB might make sense for your application.
While doing so, you may want to monitor `RubyVM::YJIT.runtime_stats[:ratio_in_yjit]` as explained above.
### Enabling YJIT lazily ### Enabling YJIT lazily
@ -287,7 +288,7 @@ This section contains tips on writing Ruby code that will run as fast as possibl
- Ruby method calls are costly. Avoid things such as methods that only return a value from a hash - Ruby method calls are costly. Avoid things such as methods that only return a value from a hash
- Try to write code so that the same variables and method arguments always have the same type - Try to write code so that the same variables and method arguments always have the same type
- Avoid using `TracePoint` as it can cause YJIT to deoptimize code - Avoid using `TracePoint` as it can cause YJIT to deoptimize code
- Avoid using `Binding` as it can cause YJIT to deoptimize code - Avoid using `binding` as it can cause YJIT to deoptimize code
You can also use the `--yjit-stats` command-line option to see which bytecodes cause YJIT to exit, and refactor your code to avoid using these instructions in the hottest methods of your code. You can also use the `--yjit-stats` command-line option to see which bytecodes cause YJIT to exit, and refactor your code to avoid using these instructions in the hottest methods of your code.