tiny.coz.experiment

1const std = @import("std");23pub const sample_period_ns: u64 = 1_000_000;4pub const sample_batch_size: u64 = 10;5pub const speedup_divisions: u64 = 20;6pub const zero_speedup_weight: u64 = 7;7pub const experiment_min_time_ns: u64 = sample_period_ns * sample_batch_size * 50;8pub const experiment_cool_off_time_ns: u64 = sample_period_ns * sample_batch_size;9pub const experiment_target_delta: u64 = 5;10pub const experiment_max_time_ns: u64 = experiment_min_time_ns * 16;1112pub const Draw = struct {13    value: u64,1415    pub fn init(value: u64) !Draw {16        if (value > maxDraw()) return error.InvalidSpeedupDraw;17        return .{ .value = value };18    }1920    pub fn maxDraw() u64 {21        return zero_speedup_weight + speedup_divisions;22    }23};2425pub const Plan = struct {26    delay_size_ns: u64,27    virtual_speedup: f64,28    duration_ns: u64,29};3031pub fn planFromDraw(draw: Draw, duration_ns: u64) Plan {32    const delay_size = delaySizeFromDraw(draw);33    return .{34        .delay_size_ns = delay_size,35        .virtual_speedup = virtualSpeedupFromDelay(delay_size),36        .duration_ns = duration_ns,37    };38}3940pub fn delaySizeFromDraw(draw: Draw) u64 {41    if (draw.value <= zero_speedup_weight) return 0;42    return (draw.value - zero_speedup_weight) * sample_period_ns / speedup_divisions;43}4445pub fn fixedDelaySize(speedup_percent: i32) ?u64 {46    if (speedup_percent < 0 or speedup_percent > 100) return null;47    return sample_period_ns * @as(u64, @intCast(speedup_percent)) / 100;48}4950pub fn virtualSpeedupFromDelay(delay_size_ns: u64) f64 {51    return @as(f64, @floatFromInt(delay_size_ns)) / @as(f64, @floatFromInt(sample_period_ns));52}5354pub fn adjustDuration(current_duration_ns: u64, min_delta: u64) u64 {55    if (min_delta < experiment_target_delta) {56        return @min(current_duration_ns * 2, experiment_max_time_ns);57    }58    if (min_delta > experiment_target_delta * 2 and current_duration_ns >= experiment_min_time_ns * 2) {59        return current_duration_ns / 2;60    }61    return current_duration_ns;62}6364pub fn correctedDurationNs(elapsed_ns: u64, inserted_delay_ns: u64, overshoot_ns: u64) u64 {65    return elapsed_ns -| inserted_delay_ns -| overshoot_ns;66}6768test "draw range matches upstream uniform distribution bounds" {69    try std.testing.expectEqual(@as(u64, 27), Draw.maxDraw());70    try std.testing.expectError(error.InvalidSpeedupDraw, Draw.init(28));71}7273test "delay size from random draw preserves upstream weighting" {74    try std.testing.expectEqual(@as(u64, 0), delaySizeFromDraw(try Draw.init(0)));75    try std.testing.expectEqual(@as(u64, 0), delaySizeFromDraw(try Draw.init(7)));76    try std.testing.expectEqual(@as(u64, 50_000), delaySizeFromDraw(try Draw.init(8)));77    try std.testing.expectEqual(@as(u64, 500_000), delaySizeFromDraw(try Draw.init(17)));78    try std.testing.expectEqual(@as(u64, 1_000_000), delaySizeFromDraw(try Draw.init(27)));79}8081test "fixed delay size accepts only percentage speedups" {82    try std.testing.expectEqual(@as(?u64, null), fixedDelaySize(-1));83    try std.testing.expectEqual(@as(?u64, null), fixedDelaySize(101));84    try std.testing.expectEqual(@as(?u64, 0), fixedDelaySize(0));85    try std.testing.expectEqual(@as(?u64, 250_000), fixedDelaySize(25));86    try std.testing.expectEqual(@as(?u64, 1_000_000), fixedDelaySize(100));87}8889test "virtual speedup is delay size divided by sample period" {90    try std.testing.expectEqual(@as(f64, 0), virtualSpeedupFromDelay(0));91    try std.testing.expectEqual(@as(f64, 0.25), virtualSpeedupFromDelay(250_000));92    try std.testing.expectEqual(@as(f64, 1), virtualSpeedupFromDelay(sample_period_ns));93}9495test "experiment duration adapts to progress-point deltas" {96    try std.testing.expectEqual(97        @as(u64, experiment_min_time_ns * 2),98        adjustDuration(experiment_min_time_ns, experiment_target_delta - 1),99    );100    try std.testing.expectEqual(101        @as(u64, experiment_max_time_ns),102        adjustDuration(experiment_max_time_ns, experiment_target_delta - 1),103    );104    try std.testing.expectEqual(105        @as(u64, experiment_min_time_ns),106        adjustDuration(experiment_min_time_ns * 2, experiment_target_delta * 2 + 1),107    );108    try std.testing.expectEqual(109        @as(u64, experiment_min_time_ns),110        adjustDuration(experiment_min_time_ns, experiment_target_delta * 2 + 1),111    );112    try std.testing.expectEqual(113        @as(u64, experiment_min_time_ns),114        adjustDuration(experiment_min_time_ns, experiment_target_delta),115    );116}117118test "corrected duration removes inserted delay and overshoot" {119    try std.testing.expectEqual(@as(u64, 70), correctedDurationNs(100, 20, 10));120    try std.testing.expectEqual(@as(u64, 0), correctedDurationNs(100, 80, 30));121}122123test "plan bundles delay speedup and duration" {124    const plan = planFromDraw(try Draw.init(12), experiment_min_time_ns);125126    try std.testing.expectEqual(@as(u64, 250_000), plan.delay_size_ns);127    try std.testing.expectEqual(@as(f64, 0.25), plan.virtual_speedup);128    try std.testing.expectEqual(@as(u64, experiment_min_time_ns), plan.duration_ns);129}

1pub const experiment = @import("experiment.zig");