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FrityetFrityet
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jit: observe first-attachment requests in pre-MT native loops
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Lines changed: 9341 additions & 6 deletions

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‎bench/jit-first-attach-poll-2026-09-05/bench-diagnostic-results.json‎

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[
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{
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"command": [
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"taskset",
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"-c",
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"0-15",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/base-normal/src/luajit",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/bench-diagnostic.lua",
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"numeric"
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],
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"LUA_PATH": "/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/base-normal/src/?.lua;/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/base-normal/src/?/init.lua;;",
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"exit": 0,
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"seconds": 0.008279687997855945
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},
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{
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"command": [
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"taskset",
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"-c",
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"0-15",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/base-normal/src/luajit",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/bench-diagnostic.lua",
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"ffi_struct"
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],
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"LUA_PATH": "/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/base-normal/src/?.lua;/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/base-normal/src/?/init.lua;;",
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"exit": 0,
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"seconds": 0.010000849000789458
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},
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{
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"command": [
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"taskset",
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"-c",
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"0-15",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/base-normal/src/luajit",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/bench-diagnostic.lua",
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"table_read"
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],
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"LUA_PATH": "/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/base-normal/src/?.lua;/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/base-normal/src/?/init.lua;;",
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"exit": 0,
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"seconds": 0.008363126002222998
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},
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{
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"command": [
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"taskset",
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"-c",
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"0-15",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/fix-normal/src/luajit",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/bench-diagnostic.lua",
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"numeric"
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],
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"LUA_PATH": "/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/fix-normal/src/?.lua;/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/fix-normal/src/?/init.lua;;",
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"exit": 0,
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"seconds": 0.008147628999722656
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},
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{
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"command": [
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"taskset",
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"-c",
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"0-15",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/fix-normal/src/luajit",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/bench-diagnostic.lua",
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"ffi_struct"
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],
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"LUA_PATH": "/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/fix-normal/src/?.lua;/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/fix-normal/src/?/init.lua;;",
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"exit": 0,
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"seconds": 0.0096651509993535
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},
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{
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"command": [
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"taskset",
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"-c",
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"0-15",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/fix-normal/src/luajit",
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"/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/bench-diagnostic.lua",
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"table_read"
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],
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"LUA_PATH": "/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/fix-normal/src/?.lua;/tmp/lj-mode0-poll-fix-20260905-qn7zwzl_/fix-normal/src/?/init.lua;;",
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"exit": 0,
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"seconds": 0.008597928001108812
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}
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]

‎bench/jit-first-attach-poll-2026-09-05/bench-diagnostic.lua‎

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local jit = require('jit')
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local util = require('jit.util')
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local case = assert(arg[1])
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local work, input, n, expected
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local exits = 0
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local function witness() exits = exits + 1 end
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jit.off(witness)
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jit.opt.start('hotloop=1', 'hotexit=255')
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jit.attach(witness, 'texit')
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if case == 'numeric' then
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n = 500000000
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work = function(count)
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local s = 0
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for i = 1, count do s = s + 1 end
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return s
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end
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expected = function(count) return count end
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elseif case == 'ffi_struct' then
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input = require('ffi').new('struct { double x; double y; }', 0, 1)
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n = 50000000
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work = function(count, p)
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p.x = 0
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local s = 0
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for i = 1, count do p.x = p.x + 1; s = p.x + p.y end
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return s
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end
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expected = function(count) return count + 1 end
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elseif case == 'table_read' then
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input = { 1, 2 }
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n = 100000000
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work = function(count, p)
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local s = 0
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for i = 1, count do s = s + p[1] + p[2] end
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return s
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end
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expected = function(count) return count * 3 end
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else
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error('unknown case')
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end
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assert(work(1000, input) == expected(1000))
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assert(exits > 0 and util.traceinfo(1), 'real native warm witness')
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do
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local bit = require('bit')
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local names = require('jit.vmdef').irnames
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local info = assert(util.traceinfo(1))
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local polls = 0
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print('case', case, 'nins', info.nins)
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for ref = 1, info.nins do
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local mode, ot, a, b = util.traceir(1, ref)
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if ot then
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local offset = bit.rshift(ot, 8) * 6
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local op = names:sub(offset+1, offset+6)
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print(ref, op, a, b)
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if op:match('^XPOLL') then assert(a == 0); polls = polls + 1 end
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end
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end
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assert(polls > 0)
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local mcode, address, loop = util.tracemc(1)
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print('mcode', #mcode, 'loop-offset', loop)
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require('jit.dis_x64').disass(mcode, address)
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return
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end
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local samples, best = {}, math.huge
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for i = 1, 5 do
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local start = os.clock()
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local result = work(n, input)
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local elapsed = os.clock() - start
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assert(result == expected(n))
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samples[i] = string.format('%.9f', elapsed)
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best = math.min(best, elapsed)
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end
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print(case, n, string.format('%.9f', best), table.concat(samples, ','), exits)

‎bench/jit-first-attach-poll-2026-09-05/bench.lua‎

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local jit = require('jit')
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local util = require('jit.util')
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local case = assert(arg[1])
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local work, input, n, expected
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local exits = 0
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local function witness() exits = exits + 1 end
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jit.off(witness)
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jit.opt.start('hotloop=1', 'hotexit=255')
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jit.attach(witness, 'texit')
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if case == 'numeric' then
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n = 500000000
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work = function(count)
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local s = 0
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for i = 1, count do s = s + 1 end
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return s
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end
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expected = function(count) return count end
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elseif case == 'ffi_struct' then
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input = require('ffi').new('struct { double x; double y; }', 0, 1)
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n = 50000000
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work = function(count, p)
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p.x = 0
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local s = 0
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for i = 1, count do p.x = p.x + 1; s = p.x + p.y end
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return s
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end
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expected = function(count) return count + 1 end
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elseif case == 'table_read' then
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input = { 1, 2 }
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n = 100000000
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work = function(count, p)
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local s = 0
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for i = 1, count do s = s + p[1] + p[2] end
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return s
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end
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expected = function(count) return count * 3 end
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else
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error('unknown case')
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end
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assert(work(1000, input) == expected(1000))
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assert(exits > 0 and util.traceinfo(1), 'real native warm witness')
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local samples, best = {}, math.huge
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for i = 1, 5 do
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local start = os.clock()
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local result = work(n, input)
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local elapsed = os.clock() - start
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assert(result == expected(n))
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samples[i] = string.format('%.9f', elapsed)
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best = math.min(best, elapsed)
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end
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print(case, n, string.format('%.9f', best), table.concat(samples, ','), exits)

‎bench/jit-first-attach-poll-2026-09-05/cost/metadata.json‎

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{
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"date": "2026-09-05",
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"cpu": 30,
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"rounds": 7,
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"samples_per_process": 5,
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"clock": "os.clock CPU seconds",
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"GC": "enabled, unchanged defaults",
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"host": {
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"system": "Linux",
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"node": "7f3bd9b38fd8",
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"release": "7.2.1-ogc4.1.fc44.x86_64",
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"version": "#1 SMP PREEMPT_DYNAMIC Tue Sep 1 22:10:56 UTC 2026",
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"machine": "x86_64",
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"processor": ""
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},
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"benchmark_sha256": "2c0bddf908f20b822ee227866734ac7bbe94da0b856f43038fb0f45839d60255",
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"binaries": {
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"base-normal": "692a47bfd7e06cd7e62c0746148b3550c020dc30a7c021b1a03303d10d654424",
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"fix-normal": "4a2fcffb7a64b8e70699175b25421b6e851c43934d7d0f52aa6f5a964509d097"
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}
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}

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