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Misc #16258

closed

[PATCH] Combine call info and cache to speed up method invocation

Added by alanwu (Alan Wu) over 4 years ago. Updated over 4 years ago.

Status:
Closed
[ruby-core:95373]

Description

Proposed change: https://github.com/ruby/ruby/pull/2564

To perform a regular method call, the VM needs two structs, rb_call_info
and rb_call_cache. At the moment, we allocate these two structures in
separate buffers. In the worst case, the CPU needs to read 4 cache lines to
complete a method call. Putting the two structures together reduces the
maximum number of cache line reads to 2.

Combining the structures also saves 8 bytes per call site as the current
layout uses separate pointers for the call info and the call cache. This
change saves about 2 MiB on Discourse.

The Optcarrot benchmark receives a performance improvement from this patch. I
collected the following results using make install binaries compiled with
-DRUBY_NDEBUG, with a sample size of 50 for each category:

master-a5245c after patch speed-up ratio
plain 42.39 50.17 18.35%
jit 71.72 72.73 1.41%

These are medium FPS from the benchmark output. For raw benchmark results and
basic stats, see
https://gist.github.com/XrXr/ce5cb7cf2c3c4d29e58c919fa5c86b33. I took these
results with a i7-8750H CPU @ 2.20GHz on a 2018 MacBook Pro. I also ran the
benchmark with a AMD 2400G running Arch Linux and observed a 3% improvement
without the jit.

Complications

  • A new instruction attribute comptime_sp_inc is introduced to calculate
    SP increase at compile time without using call caches. At compile time, a
    TS_CALLDATA operand points to a call info struct, but at runtime, the
    same operand points to a call data struct. Instruction that explicitly
    define sp_inc also need to define comptime_sp_inc.
  • MJIT code for copying call cache becomes slightly more complicated.
  • This changes the bytecode format, which might break existing tools.

I think this patch offers a good general performance boost for a manageable amount
of code change.

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