Struct DerivedMetricDef 

#[non_exhaustive]
pub struct DerivedMetricDef {
    pub name: &'static str,
    pub ladder: ScaleLadder,
    pub description: &'static str,
    pub inputs: &'static [&'static str],
    pub is_ratio: bool,
    pub compute: fn(&BTreeMap<String, Aggregated>) -> Option<DerivedValue>,
    pub section: Section,
}

Definition of a derived metric: a function that consumes the already-aggregated input metrics for a group and produces a single scalar (with its own unit and operator-facing description).

The compute fn returns None when an input metric is missing from the group’s metrics map (capture-side gated by a kernel CONFIG that wasn’t enabled, or jemalloc not linked) OR when the formula would divide by zero. The renderer surfaces a None cell as - so the operator can distinguish “not computable” from “computed as zero”.

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

name: &'static str

ladder: ScaleLadder

Auto-scale ladder for the cell. ScaleLadder::None for ratio rows (renders as a bare three-decimal scalar with no suffix), ScaleLadder::Ns / ScaleLadder::Bytes / etc. for unit-bearing derivations. The same closed-match dispatch AggRule::ladder feeds.

description: &'static str

Operator-facing one-line description; surfaced by the ctprof metric-list subcommand.

inputs: &'static [&'static str]

Names of input metrics from CTPROF_METRICS. Pure documentation — surfaces in the metric-list output so the operator sees what each derivation depends on.

is_ratio: bool

Render-shape flag for dimensionless quantities. When true, the renderer (1) suppresses the % (delta_pct) column, (2) renders the value as N.NNN with three decimals instead of routing through the auto-scale ladder, and (3) renders the delta as +/-N.NNN (no scaled unit suffix).

The [0, 1] interval is the common case where this flag applies: cpu_efficiency, affine_success_ratio, and involuntary_csw_ratio all live in [0, 1]. Delta on a [0, 1] ratio reads as percentage points (0.5 → 0.6 = +0.100 = +10pp), and delta / baseline as a fraction (the % column) becomes confusing — +20% on a [0, 1] ratio is already in percentage points, so a percentage-of-percentage readout double-encodes the signal.

disk_io_fraction (range [0, ∞)) carries is_ratio: true for the rendering shape but does NOT satisfy the percentage-points interpretation: a value of 1.5 is possible (readahead pulls more block-device bytes than the syscall requested), so a delta of +0.100 reads as “ratio rose by 0.1” rather than “ratio rose by 10 percentage points.” The render shape is still correct (suppress %, three decimals, no auto-scale) — only the pp interpretation is invalid.

compute: fn(&BTreeMap<String, Aggregated>) -> Option<DerivedValue>

The computation. Pulls input scalars from the group’s metrics map via Aggregated::numeric() and produces the derived scalar.

section: Section

Section this derived metric belongs to for the --sections per-row filter, mirroring CtprofMetricDef::section. Most derivations tag Section::Derived; the 9 derivations whose inputs are taskstats fields (the eight avg_*_delay_ns averages plus total_offcpu_delay_ns) tag Section::TaskstatsDelay so an operator running --sections taskstats-delay gets a full taskstats view — the 34 raw rows AND the 9 derivations that depend on them — without dragging in unrelated derived metrics. The ## Derived metrics table emitter checks DisplayOptions::is_section_enabled per row before rendering, and the outer-table gate opens whenever EITHER section in the rendered set is enabled.

Trait Implementations

impl Clone for DerivedMetricDef

fn clone(&self) -> DerivedMetricDef

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for DerivedMetricDef

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Copy for DerivedMetricDef