[ruby-core:85968] [Ruby trunk Feature#14489] MJIT needs a reusable cache

Issue #14489 has been updated by k0kubun (Takashi Kokubun).


We should make sure what we're going to solve here first before introducing such mechanism. At least I prefer having Feature#14492 first and I suspect boot time would not be the issue after that. With --jit enabled, it takes time to wait for shutting down MJIT worker and it's sometimes considered as kind of boot time issue for short running scripts, but it's totally different issue from this ticket.

And I also suspect that the cached code might be inefficient because some aggressive optimization using cache like class_serial would be unavailable. Just translating instructions to native code wouldn't make big difference from VM execution, and we need inlining which depends on cache key that can't be known before execution. Then it may become even slower than original ISeq execution by increasing the number of VM invocations.

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Feature #14489: MJIT needs a reusable cache
https://bugs.ruby-lang.org/issues/14489#change-70834

* Author: sam.saffron (Sam Saffron)
* Status: Rejected
* Priority: Normal
* Assignee: k0kubun (Takashi Kokubun)
* Target version: 
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Currently on Discourse boot I notice a few minutes of jitting every time you boot it:

This is a redacted output: https://gist.github.com/SamSaffron/4e18c2dacf476f1f27275f5b5d7bbb97 

CPU is spinning hard compiling temp file after temp file for **minutes**:

> JIT success (213.1ms): platform_string@/home/sam/.rbenv/versions/master/lib/ruby/gems/2.6.0/gems/bundler-1.16.1/lib/bundler/lazy_specification.rb:18 -> /tmp/_ruby_mjit_p6914u199.c

and so on.

Instead, mjit should have a reusable cache on disk it first tries fetching from prior to re-compiling. It can use an ISEQ SHA1 hash as the key to the cache. 






---Files--------------------------------
14489.patch (29.8 KB)


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