From: pdahorek@... Date: 2019-07-31T18:51:52+00:00 Subject: [ruby-core:94082] [Ruby master Feature#15631] Let round_capa for ID table not allocate excess capacity for power of 2 ints >= 4 Issue #15631 has been updated by ahorek (Pavel Rosick�). I run several benchmark suites for both patches https://github.com/ruby-bench/ruby-bench-suite https://github.com/schneems/derailed_benchmarks but all differences were within margin of error. Here's an optimized assembly comparsion that explains why: https://user-images.githubusercontent.com/9540855/62237913-2e221380-b3d2-11e9-932a-14b09038bf91.png saving 1-2 instructions makes no real difference. feel free to close the issue. Thanks ---------------------------------------- Feature #15631: Let round_capa for ID table not allocate excess capacity for power of 2 ints >= 4 https://bugs.ruby-lang.org/issues/15631#change-80313 * Author: ahorek (Pavel Rosick�) * Status: Open * Priority: Normal * Assignee: ko1 (Koichi Sasada) * Target version: ---------------------------------------- right now round_capa value is rounded up to the next power of 2 ``` round_capa(4) -> returns 8 round_capa(8) -> returns 16 round_capa(16) -> returns 32 round_capa(5) -> returns 8 round_capa(9) -> returns 16 round_capa(17) -> returns 32 etc. ``` it seems wasteful to allocate the extra items capacity, so this PR changes that to ``` round_capa(4) -> returns 4 round_capa(8) -> returns 8 round_capa(16) -> returns 16 round_capa(5) -> returns 8 round_capa(9) -> returns 16 round_capa(17) -> returns 32 etc. ``` the main purpose is to reduce memory usage especially during boot my patch also uses BUILTIN_CLZ macro instead of shifts that makes it slightly faster here's a benchmark ```ruby require 'benchmark/ips' Benchmark.ips do |x| x.config(time: 20, warmup: 3) x.report('struct', "Struct.new(*('a'..'z').map { |x| x.to_sym })") end ``` ``` trunk Warming up -------------------------------------- struct 527.000 i/100ms Calculating ------------------------------------- struct 5.461k (� 5.5%) i/s - 109.089k in 20.040253s methodmising - POW2_P (github) Warming up -------------------------------------- struct 544.000 i/100ms Calculating ------------------------------------- struct 5.570k (� 4.1%) i/s - 111.520k in 20.057245s ahorek - BUILTIN_CLZ (id_table.c.patch) Warming up -------------------------------------- struct 571.000 i/100ms Calculating ------------------------------------- struct 5.812k (� 3.6%) i/s - 116.484k in 20.070607s ``` discussion https://github.com/ruby/ruby/pull/2083 ---Files-------------------------------- id_table.c.patch (534 Bytes) st.c.patch (455 Bytes) st.c.patch (434 Bytes) -- https://bugs.ruby-lang.org/ Unsubscribe: