open-standards/proof/proof-rs/crates/proof-cascade/tests/rapl_hardware.rs

//! Linux RAPL against the hardware: this host's powercap counters, read by
//! the meter and by an oracle the tests declare here.
//!
//! In a test binary of its own, so the RAPL probe behind `rapl_status()`
//! runs in this process, and the tests take one lock: each burns CPU and
//! reads machine-wide counters. The oracle reads `/sys/class/powercap`
//! itself — every zone's `name`, `energy_uj` and `max_energy_range_uj` — and
//! applies the sustained-advance rule to the top-level `package-<n>` zones
//! on its own. None of these tests passes without asserting: where the
//! counters cannot be read (no powercap; a CI container, whose
//! `/sys/devices/virtual/powercap` Docker masks), the status must say so and
//! agree with the oracle; where they are live, both must say live, RAPL must
//! be the meter's source, and the marginal figure of a burn on every spare
//! core must be `HwShunt`, claim the CPU package and not the GPU, and, summed
//! over the calls, fit inside the oracle's package-only bracket around the
//! whole measurement (idle and busy windows), which a figure that added
//! psys or a package's core sub-zone overruns.
//!
//! A package zone is one named `package-<n>`, or, on a multi-die Intel
//! package, each die's `package-<n>-die-<m>`. Where powercap lists no package
//! (a kernel without the powercap driver), the meter reads each RAPL domain's
//! energy-status MSR instead, and so does the oracle, with its own reader:
//! each die on Intel and each package on AMD and Hygon, as Linux scopes them,
//! read on its lowest-numbered CPU's `/dev/cpu/<n>/msr` at the vendor's
//! registers, the 32-bit count at the domain's unit. Those domains join the
//! oracle's zones as `msr-package:<p>` or `msr-package:<p>-die-<d>`, named
//! `package-<p>` or `package-<p>-die-<d>`, and every test above runs over
//! them unchanged; without `CAP_SYS_RAWIO` they do not read, and the status
//! must say so.

#![cfg(target_os = "linux")]

use std::path::Path;
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::{Mutex, MutexGuard};
use std::time::{Duration, Instant};

use proof_cascade::meter::{self, rapl_status, CounterStatus, MeterSource};
use proof_schema::Provenance;

/// One test at a time: each burns CPU and reads machine-wide counters.
static SERIAL: Mutex<()> = Mutex::new(());

fn serial() -> MutexGuard<'static, ()> {
    SERIAL.lock().unwrap_or_else(|poisoned| poisoned.into_inner())
}

/// The tests' own reading of `/sys/class/powercap`: every zone listed, its
/// `name`, `energy_uj` and `max_energy_range_uj`, read here and nowhere else,
/// and the sustained-advance verdict over the package zones by the family's
/// rule. Nothing in it comes from the crate under test.
#[allow(dead_code)]
mod oracle {
    use std::os::raw::{c_int, c_long};
    use std::path::{Path, PathBuf};
    use std::time::{Duration, Instant};

    /// Where the kernel lists its powercap zones.
    pub const POWERCAP: &str = "/sys/class/powercap";

    #[repr(C)]
    struct Timespec {
        tv_sec: c_long,
        tv_nsec: c_long,
    }

    unsafe extern "C" {
        fn clock_gettime(clock_id: c_int, tp: *mut Timespec) -> c_int;
    }

    /// `CLOCK_THREAD_CPUTIME_ID` in Linux `<linux/time.h>`.
    const CLOCK_THREAD_CPUTIME_ID: c_int = 3;

    /// This thread's CPU time.
    pub fn thread_cpu() -> Duration {
        let mut ts = Timespec { tv_sec: 0, tv_nsec: 0 };
        assert_eq!(unsafe { clock_gettime(CLOCK_THREAD_CPUTIME_ID, &mut ts) }, 0, "clock_gettime");
        Duration::new(ts.tv_sec as u64, ts.tv_nsec as u32)
    }

    /// Spin this thread until it has used `d` of its own CPU time, or `wall_cap`
    /// of wall time has passed. Returns the CPU it got.
    pub fn burn(d: Duration, wall_cap: Duration) -> Duration {
        let (started, wall) = (thread_cpu(), Instant::now());
        let mut acc: u64 = 0;
        while thread_cpu() - started < d && wall.elapsed() < wall_cap {
            for _ in 0..1_000 {
                acc = std::hint::black_box(acc.wrapping_add(1));
            }
        }
        thread_cpu() - started
    }

    /// One entry of the powercap directory, or one package's energy-status
    /// MSR where powercap lists no package.
    #[derive(Debug, Clone)]
    pub struct Zone {
        /// The directory entry: `intel-rapl:0`, `intel-rapl:0:0`, `intel-rapl-mmio:0`, ...;
        /// `msr-package:<id>` for an MSR package.
        pub dir: String,
        pub name: Option<String>,
        pub energy_uj: Option<u64>,
        pub max_uj: Option<u64>,
        /// How to read an MSR package; `None` for a powercap entry.
        pub msr: Option<Msr>,
    }

    /// One package's energy-status MSR, as the oracle reads it.
    #[derive(Debug, Clone)]
    pub struct Msr {
        /// `/dev/cpu/<the package's lowest-numbered CPU>/msr`.
        pub device: PathBuf,
        /// The energy-status register: 0x611 (Intel), 0xC001029B (AMD, Hygon).
        pub register: u64,
        /// The unit: 2^-shift J per count, bits 12:8 of the power-unit MSR.
        pub shift: u32,
    }

    /// The 8 bytes at offset `register` of the `msr` device file `device`.
    fn msr_read(device: &Path, register: u64) -> Option<u64> {
        use std::os::unix::fs::FileExt;
        let mut b = [0u8; 8];
        std::fs::File::open(device).ok()?.read_exact_at(&mut b, register).ok()?;
        Some(u64::from_le_bytes(b))
    }

    /// The microjoules in the 32-bit count of `raw`, at 2^-shift J a count.
    fn msr_uj(raw: u64, shift: u32) -> u64 {
        (u128::from(raw & 0xFFFF_FFFF) * 1_000_000 / (1u128 << shift)) as u64
    }

    /// This host's RAPL domains' energy-status MSRs, as zones: each die on
    /// Intel family 6 (0x606 / 0x611; `die_id` within `physical_package_id`,
    /// 0 where the kernel lists none), `msr-package:<p>-die-<d>` named
    /// `package-<p>-die-<d>`; each package on AMD family 0x17 and later and
    /// Hygon (0xC0010299 / 0xC001029B), `msr-package:<p>` named
    /// `package-<p>`. Each read on its lowest-numbered CPU, wrapping at 2^32
    /// counts. Empty unless every domain's power unit reads, and none is zero.
    fn msr_packages() -> Vec<Zone> {
        let Some(cpuinfo) = text(PathBuf::from("/proc/cpuinfo")) else { return Vec::new() };
        let value = |key: &str| {
            cpuinfo.lines().find_map(|l| l.split_once(':').filter(|(k, _)| k.trim() == key).map(|(_, v)| v.trim().to_string()))
        };
        let (Some(vendor), Some(family)) = (value("vendor_id"), value("cpu family").and_then(|f| f.parse::<u32>().ok())) else {
            return Vec::new();
        };
        let (unit_register, register, per_die) = match (vendor.as_str(), family) {
            ("GenuineIntel", 6) => (0x606, 0x611, true),
            ("AuthenticAMD" | "HygonGenuine", f) if f >= 0x17 => (0xC001_0299, 0xC001_029B, false),
            _ => return Vec::new(),
        };
        let mut first = std::collections::BTreeMap::<(u64, Option<u64>), u64>::new();
        for e in std::fs::read_dir("/sys/devices/system/cpu").into_iter().flatten().flatten() {
            let name = e.file_name().to_string_lossy().into_owned();
            let Some(cpu) = name.strip_prefix("cpu").and_then(|n| n.parse::<u64>().ok()) else { continue };
            let Some(package) = number(e.path().join("topology/physical_package_id")) else { continue };
            let die = per_die.then(|| number(e.path().join("topology/die_id")).unwrap_or(0));
            first.entry((package, die)).and_modify(|c| *c = (*c).min(cpu)).or_insert(cpu);
        }
        let mut zones = Vec::new();
        for ((package, die), cpu) in first {
            let device = PathBuf::from(format!("/dev/cpu/{cpu}/msr"));
            let Some(unit) = msr_read(&device, unit_register) else { return Vec::new() };
            let shift = ((unit >> 8) & 0x1F) as u32;
            if shift == 0 {
                return Vec::new();
            }
            let (dir, name) = match die {
                Some(d) => (format!("msr-package:{package}-die-{d}"), format!("package-{package}-die-{d}")),
                None => (format!("msr-package:{package}"), format!("package-{package}")),
            };
            zones.push(Zone {
                dir,
                name: Some(name),
                energy_uj: msr_read(&device, register).map(|raw| msr_uj(raw, shift)),
                max_uj: Some(((1u128 << 32) * 1_000_000 / (1u128 << shift)) as u64),
                msr: Some(Msr { device, register, shift }),
            });
        }
        zones
    }

    fn text(p: PathBuf) -> Option<String> {
        std::fs::read_to_string(p).ok().map(|s| s.trim().to_string())
    }

    fn number(p: PathBuf) -> Option<u64> {
        text(p)?.parse().ok()
    }

    /// Every entry under `root`, in name order; and, where none of them is a
    /// package, this host's package energy-status MSRs that read.
    pub fn zones(root: &Path) -> Vec<Zone> {
        let mut zones: Vec<Zone> = match std::fs::read_dir(root) {
            Ok(entries) => entries
                .flatten()
                .map(|e| {
                    let dir = e.file_name().to_string_lossy().into_owned();
                    let p = e.path();
                    Zone {
                        name: text(p.join("name")),
                        energy_uj: number(p.join("energy_uj")),
                        max_uj: number(p.join("max_energy_range_uj")),
                        msr: None,
                        dir,
                    }
                })
                .collect(),
            Err(_) => Vec::new(),
        };
        zones.sort_by(|a, b| a.dir.cmp(&b.dir));
        if !zones.iter().any(is_package) {
            zones.extend(msr_packages());
        }
        zones
    }

    fn digits(s: &str) -> bool {
        !s.is_empty() && s.bytes().all(|b| b.is_ascii_digit())
    }

    /// A top-level RAPL zone: `intel-rapl:<n>`. Not a sub-zone, not MMIO.
    pub fn top_level(z: &Zone) -> bool {
        z.dir.strip_prefix("intel-rapl:").is_some_and(digits)
    }

    /// A package zone: top-level, named `package-<n>`, or `package-<n>-die-<m>`
    /// (one die of a multi-die package); or an MSR domain.
    pub fn is_package(z: &Zone) -> bool {
        let named = |n: &str| match n.strip_prefix("package-") {
            Some(rest) => match rest.split_once("-die-") {
                Some((p, d)) => digits(p) && digits(d),
                None => digits(rest),
            },
            None => false,
        };
        z.msr.is_some() || (top_level(z) && z.name.as_deref().is_some_and(named))
    }

    /// The platform zone.
    pub fn is_psys(z: &Zone) -> bool {
        top_level(z) && z.name.as_deref() == Some("psys")
    }

    /// A package's `core` sub-zone (`intel-rapl:<n>:<m>` named `core`).
    pub fn is_core(z: &Zone) -> bool {
        z.dir.strip_prefix("intel-rapl:").is_some_and(|r| r.contains(':')) && z.name.as_deref() == Some("core")
    }

    /// One zone's energy between two reads, modulo its own range.
    pub fn delta(e0: u64, e1: u64, max: Option<u64>) -> Option<u64> {
        if e1 >= e0 {
            Some(e1 - e0)
        } else {
            max.filter(|&m| m > 0)?.checked_sub(e0)?.checked_add(e1)
        }
    }

    /// `energy_uj` of each of `dirs` under `root` (an MSR package's count, at
    /// its unit), in order; `None` if any fails.
    pub fn read(root: &Path, dirs: &[&Zone]) -> Option<Vec<u64>> {
        dirs.iter()
            .map(|z| match &z.msr {
                Some(m) => msr_read(&m.device, m.register).map(|raw| msr_uj(raw, m.shift)),
                None => number(root.join(&z.dir).join("energy_uj")),
            })
            .collect()
    }

    /// The summed energy of `which` of `set` between two reads of `set`.
    pub fn energy(set: &[&Zone], before: &[u64], after: &[u64], which: impl Fn(&Zone) -> bool) -> u64 {
        set.iter()
            .zip(before.iter().zip(after))
            .filter(|(z, _)| which(z))
            .map(|(z, (&b, &a))| delta(b, a, z.max_uj).expect("a zone fell with no readable range"))
            .sum()
    }

    /// What the oracle concluded about the package counters under a root.
    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
    pub enum Verdict {
        /// No top-level zone's `energy_uj` reads (no powercap, a masked or
        /// root-only tree).
        Unreadable,
        /// Top-level zones read, but none is a package.
        NoPackage,
        /// Every package read, but not every one kept advancing.
        Frozen,
        /// Every package advanced in at least five intervals, at least 80% of
        /// them, over at least 300 ms.
        Live,
    }

    /// The oracle's sustained-advance run over the package zones under `root`.
    #[derive(Debug)]
    pub struct Watch {
        pub verdict: Verdict,
        pub packages: Vec<String>,
        pub intervals: u32,
        pub advances: Vec<u32>,
        pub window: Duration,
    }

    impl Watch {
        /// The verdict and each package's advances, for the test's log line.
        pub fn summary(&self) -> String {
            let per: Vec<String> =
                self.packages.iter().zip(&self.advances).map(|(p, a)| format!("{p} advanced {a}/{}", self.intervals)).collect();
            format!("{:?} ({} over {} ms)", self.verdict, per.join(", "), self.window.as_millis())
        }
    }

    /// Sample every package's `energy_uj`, burning 25 ms of this thread's CPU
    /// between samples (capped at 500 ms of wall time), until every package
    /// has advanced in at least five intervals, at least 80% of those
    /// observed, over at least 300 ms; or one second has passed with at least
    /// five intervals; or five seconds have.
    pub fn watch(root: &Path) -> Watch {
        let all = zones(root);
        let packages: Vec<&Zone> = all.iter().filter(|z| is_package(z)).collect();
        let names: Vec<String> = packages.iter().map(|z| z.dir.clone()).collect();
        let none = |verdict| Watch { verdict, packages: names.clone(), intervals: 0, advances: Vec::new(), window: Duration::ZERO };
        if packages.is_empty() {
            let readable = all.iter().any(|z| top_level(z) && z.energy_uj.is_some());
            return none(if readable { Verdict::NoPackage } else { Verdict::Unreadable });
        }
        let started = Instant::now();
        let Some(mut prev) = read(root, &packages) else { return none(Verdict::Unreadable) };
        let mut advances = vec![0u32; packages.len()];
        let mut intervals = 0u32;
        let live = |adv: &[u32], n: u32, w: Duration| {
            w >= Duration::from_millis(300) && adv.iter().all(|&a| a >= 5 && u64::from(a) * 5 >= u64::from(n) * 4)
        };
        loop {
            let el = started.elapsed();
            if live(&advances, intervals, el) || el >= Duration::from_secs(5) || (el >= Duration::from_secs(1) && intervals >= 5) {
                break;
            }
            burn(Duration::from_millis(25), Duration::from_millis(500));
            if let Some(now) = read(root, &packages) {
                intervals += 1;
                for ((a, n), p) in advances.iter_mut().zip(&now).zip(&prev) {
                    *a += u32::from(n > p);
                }
                prev = now;
            }
        }
        let window = started.elapsed();
        let verdict = if live(&advances, intervals, window) { Verdict::Live } else { Verdict::Frozen };
        Watch { verdict, packages: names, intervals, advances, window }
    }

    /// The zones under `root`, as one line for the log.
    pub fn listing(root: &Path) -> String {
        zones(root)
            .iter()
            .map(|z| {
                let kind = if is_package(z) {
                    "package"
                } else if is_psys(z) {
                    "psys"
                } else if is_core(z) {
                    "core sub-zone"
                } else if top_level(z) {
                    "top-level"
                } else {
                    "not summed"
                };
                let e = z.energy_uj.map_or("unreadable".to_string(), |e| e.to_string());
                let m = z.max_uj.map_or("-".to_string(), |m| m.to_string());
                format!("{}={} [{kind}] energy_uj={e} max={m}", z.dir, z.name.as_deref().unwrap_or("?"))
            })
            .collect::<Vec<_>>()
            .join("; ")
    }

    /// The CI container's view of the host's powercap directory: the same
    /// entries, each a symlink into `/sys/devices/virtual/powercap`, which
    /// Docker masks with an empty tmpfs, so every target is missing. Built
    /// from this host's own listing; removed when dropped.
    pub struct MaskedView(pub PathBuf);

    impl MaskedView {
        /// Build the masked view of this host's powercap entries in a
        /// temporary directory named by `tag` and this process.
        pub fn of_host(tag: &str) -> MaskedView {
            let root = std::env::temp_dir().join(format!("{tag}-masked-powercap-{}", std::process::id()));
            let _ = std::fs::remove_dir_all(&root);
            std::fs::create_dir_all(&root).expect("create the masked view");
            let masked = root.join("masked-devices-virtual-powercap");
            for z in zones(Path::new(POWERCAP)).iter().filter(|z| z.msr.is_none()) {
                std::os::unix::fs::symlink(masked.join(&z.dir), root.join(&z.dir)).expect("symlink");
            }
            MaskedView(root)
        }
    }

    impl Drop for MaskedView {
        fn drop(&mut self) {
            let _ = std::fs::remove_dir_all(&self.0);
        }
    }

    /// A bracket of reads around the meter's two reads: every package, psys
    /// and core zone read at four points, outer and inner on each side.
    pub struct Bracket<'a> {
        pub set: Vec<&'a Zone>,
        pub reads: [Vec<u64>; 4],
    }

    impl Bracket<'_> {
        /// The packages' energy over the outer bracket, in µJ: the most a
        /// package-only figure read inside it can be.
        pub fn package_outer(&self) -> u64 {
            energy(&self.set, &self.reads[0], &self.reads[3], is_package)
        }
        /// The packages' energy over the inner bracket, in µJ: the least a
        /// package-only figure read around it can be.
        pub fn package_inner(&self) -> u64 {
            energy(&self.set, &self.reads[1], &self.reads[2], is_package)
        }
        /// The psys zone's energy over the inner bracket, in µJ.
        pub fn psys_inner(&self) -> u64 {
            energy(&self.set, &self.reads[1], &self.reads[2], is_psys)
        }
        /// The core sub-zones' energy over the inner bracket, in µJ.
        pub fn core_inner(&self) -> u64 {
            energy(&self.set, &self.reads[1], &self.reads[2], is_core)
        }
        /// Whether the bracket read a zone of the kind `which` picks.
        pub fn has(&self, which: impl Fn(&Zone) -> bool) -> bool {
            self.set.iter().any(|z| which(z))
        }
    }

    /// The family's rule on a figure `uj` the meter read between the
    /// bracket's inner and outer reads: no less than the packages' energy
    /// over the inner bracket, no more than over the outer one, and below
    /// package+psys and package+core where those zones exist. A figure that
    /// added a zone reads at least the packages' and that zone's energy over
    /// the inner bracket, so `uj < inner + zone` is the double-count test; it
    /// can only be put where the zone moved more over the burn than the
    /// packages did in the gap between the outer and inner reads (else a
    /// correct figure could reach it too), and the line says when it could
    /// not. Returns the figures, for the log.
    pub fn assert_package_only(b: &Bracket, uj: u64) -> String {
        let (inner, outer, psys, core) = (b.package_inner(), b.package_outer(), b.psys_inner(), b.core_inner());
        let gap = outer - inner;
        let mut line = format!(
            "meter {uj} µJ; oracle package-only inner {inner} outer {outer} µJ (gap {gap}); psys inner {psys} µJ; \
             core inner {core} µJ"
        );
        assert!(inner > 0, "the packages did not advance over the burn: {line}");
        assert!(inner <= uj && uj <= outer, "the figure is outside the package-only bracket: {line}");
        for (zone, present, moved) in [("psys", b.has(is_psys), psys), ("core", b.has(is_core), core)] {
            if !present {
                continue;
            }
            assert!(moved > 0, "{zone} did not advance: {line}");
            if moved > gap {
                assert!(uj < inner + moved, "the figure reaches package+{zone}: {zone} was added: {line}");
                line.push_str(&format!("; below package+{zone}"));
            } else {
                line.push_str(&format!("; {zone} moved less than the gap, so only the outer bound tests it"));
            }
        }
        line
    }

    /// Every package, psys and core zone of `all` whose counter reads.
    pub fn bracket_set(all: &[Zone]) -> Vec<&Zone> {
        all.iter().filter(|z| (is_package(z) || is_psys(z) || is_core(z)) && z.energy_uj.is_some()).collect()
    }

    /// One oracle read of every zone of `set`; panics if one fails.
    pub fn read_all(set: &[&Zone]) -> Vec<u64> {
        read(Path::new(POWERCAP), set).expect("an oracle read of the bracket zones")
    }

    /// Read the bracket around `meter_read` (called twice) and `work`:
    /// outer, meter, inner, work, inner, meter, outer.
    pub fn around<'a, M>(set: Vec<&'a Zone>, mut meter_read: impl FnMut() -> M, work: impl FnOnce()) -> (Bracket<'a>, M, M) {
        let o0 = read_all(&set);
        let m0 = meter_read();
        let o1 = read_all(&set);
        work();
        let o2 = read_all(&set);
        let m1 = meter_read();
        let o3 = read_all(&set);
        (Bracket { set, reads: [o0, o1, o2, o3] }, m0, m1)
    }
}

use oracle::Verdict;

/// The status agrees with the oracle's own verdict, and RAPL is the meter's
/// source exactly when it is live.
#[test]
fn the_rapl_status_agrees_with_the_oracle_and_gates_the_source() {
    let _one = serial();
    let status = rapl_status();
    let watch = oracle::watch(Path::new(oracle::POWERCAP));
    let source = meter::meter_source();
    eprintln!(
        "rapl hardware: {}; oracle {}; status={status:?} source={source:?}",
        oracle::listing(Path::new(oracle::POWERCAP)),
        watch.summary()
    );
    assert_eq!(status == CounterStatus::Live, watch.verdict == Verdict::Live, "the status disagrees with the oracle");
    match watch.verdict {
        Verdict::Unreadable => assert_eq!(status, CounterStatus::Unavailable),
        Verdict::NoPackage => assert_eq!(status, CounterStatus::Absent),
        Verdict::Frozen => assert_eq!(status, CounterStatus::Frozen),
        Verdict::Live => {}
    }
    assert_eq!(source == Some(MeterSource::Rapl), status == CounterStatus::Live, "selection disagrees with the status");
    assert_eq!(meter::hardware_meter_available(), status == CounterStatus::Live);
}

/// Calls of [`ten_ms_of_work`] completed in this process.
static CALLS: AtomicU64 = AtomicU64::new(0);

/// About 10 ms of one thread's CPU work, counted.
fn ten_ms_of_work() {
    let t = Instant::now();
    let mut acc: u64 = 0;
    while t.elapsed() < Duration::from_millis(10) {
        for _ in 0..1_000 {
            acc = std::hint::black_box(acc.wrapping_add(1));
        }
    }
    CALLS.fetch_add(1, Ordering::SeqCst);
}

/// A burn on every spare core meters as a hardware figure of the CPU
/// package: `HwShunt`, from RAPL, claiming package energy and not the GPU.
/// The figure is a marginal per call (busy power over idle, times the busy
/// window, over the calls), so the calls' total can be no more than the
/// packages' energy over the whole measurement, which the oracle reads
/// around it; on a quiet host a figure that also summed a package's core
/// sub-zone (or psys, where psys tracks load) is about twice the busy margin
/// and overruns it. A figure of 0 is the crate's "inside the idle noise", and
/// is what a host whose other work holds the package at its power limit
/// reads. Where RAPL is not live there is no figure, and `work` never runs.
#[test]
fn an_all_core_burn_meters_inside_the_package_only_bracket() {
    let _one = serial();
    let all = oracle::zones(Path::new(oracle::POWERCAP));
    let set = oracle::bracket_set(&all);
    if meter::meter_source() != Some(MeterSource::Rapl) {
        let before = CALLS.load(Ordering::SeqCst);
        let m = meter::measure_marginal(ten_ms_of_work);
        let watch = oracle::watch(Path::new(oracle::POWERCAP));
        eprintln!("rapl burn: no RAPL source; figure {m:?}; oracle {}", watch.summary());
        assert_eq!(m, None, "a figure with RAPL declined");
        assert_eq!(CALLS.load(Ordering::SeqCst), before, "the work ran with RAPL declined");
        assert_ne!(watch.verdict, Verdict::Live, "the oracle saw live packages, yet RAPL is not the source");
        return;
    }
    let wall = Instant::now();
    let c0 = CALLS.load(Ordering::SeqCst);
    let o0 = oracle::read_all(&set);
    let m = meter::measure_marginal(ten_ms_of_work).expect("a live RAPL source metered the burn");
    let o3 = oracle::read_all(&set);
    let calls = CALLS.load(Ordering::SeqCst) - c0;
    let outer = oracle::energy(&set, &o0, &o3, oracle::is_package);
    let core = oracle::energy(&set, &o0, &o3, oracle::is_core);
    let psys = oracle::energy(&set, &o0, &o3, oracle::is_psys);
    let total = m.uj * calls;
    let energy = m.energy();
    eprintln!(
        "rapl burn: {calls} calls in {:?}; {} µJ a call, {total} µJ over the calls; oracle package-only {outer} µJ \
         around the measurement (idle and busy), core {core} µJ, psys {psys} µJ; energy {energy:?}; domain {:?}",
        wall.elapsed(),
        m.uj,
        m.source.domain()
    );
    assert_eq!(m.source, MeterSource::Rapl);
    assert_eq!(energy.provenance, Provenance::HwShunt);
    assert_eq!(energy.measured_uj, Some(m.uj));
    let domain = m.source.domain();
    assert!(domain.contains("package") && !domain.contains("GPU"), "the RAPL figure claims {domain}");
    assert!(calls > 0, "the work never ran");
    assert!(outer > 0, "the packages did not advance");
    // Each call's figure is rounded to the microjoule: half a microjoule a call.
    assert!(total <= outer + calls / 2 + 1, "{total} µJ over the calls overruns the packages' {outer} µJ");
    if m.uj == 0 {
        // The crate's contract: from a bracket, 0 means the busy window drew no
        // more than the idle one. On a runner whose other jobs hold the package
        // at its power limit through both windows, that is what it reads.
        eprintln!("rapl burn: the busy window drew no more than the idle one (load {:?}): inside the idle noise", loadavg());
    }
}

/// The host's load averages, for the log.
fn loadavg() -> Option<String> {
    std::fs::read_to_string("/proc/loadavg").ok().map(|s| s.trim().to_string())
}