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//! Kinds of CPU cores
//!
//! This module lets you handle platforms with heterogeneous CPU cores, such as
//! [ARM big.LITTLE](https://fr.wikipedia.org/wiki/Big.LITTLE) and [Intel Adler
//! Lake](https://fr.wikipedia.org/wiki/Alder_Lake).
//!
//! Using it, you can query how many different kinds of CPUs are present on the
//! platform, which kind maps into which OS-exposed logical CPUs, and how these
//! CPU kinds differ from each other (power efficiency, clock speed, etc).
//!
//! Most of this module's functionality is exposed via [methods of the Topology
//! struct](../../topology/struct.Topology.html#kinds-of-cpu-cores). The module
//! itself only hosts type definitions that are related to this functionality.
#[cfg(doc)]
use crate::topology::support::DiscoverySupport;
use crate::{
cpu::cpuset::CpuSet,
errors::{self},
ffi::{int, string::LibcString, transparent::AsNewtype},
info::TextualInfo,
topology::{editor::TopologyEditor, Topology},
};
use derive_more::Display;
use hwlocality_sys::hwloc_info_s;
#[allow(unused)]
#[cfg(test)]
use similar_asserts::assert_eq;
use std::{
ffi::{c_int, c_uint},
iter::FusedIterator,
num::NonZeroUsize,
ops::Deref,
ptr,
};
use thiserror::Error;
/// # Kinds of CPU cores
///
/// Platforms with heterogeneous CPUs may have some cores with different
/// features or frequencies. This API exposes identical PUs in sets called CPU
/// kinds. Each PU of the topology may only be in a single kind.
///
/// The number of kinds may be obtained with [`num_cpu_kinds()`]. If the
/// platform is homogeneous, there may be a single kind with all PUs. If the
/// platform or operating system does not expose any information about CPU
/// cores, there may be no kind at all.
///
/// Information about CPU kinds can also be enumerated using [`cpu_kinds()`].
/// For each CPU kind, an abstracted efficiency value is provided, along with
/// [info attributes](https://hwloc.readthedocs.io/en/v2.9/topoattrs.html#topoattrs_cpukinds)
/// such as "CoreType" or "FrequencyMaxMHz".
///
/// A higher efficiency value means greater intrinsic performance (and possibly
/// less performance/power efficiency). Kinds with lower efficiency values are
/// ranked first: the first CPU kind yielded by [`cpu_kinds()`] describes CPUs
/// with lower performance but higher energy-efficiency. Later CPU kinds would
/// rather describe power-hungry high-performance cores.
///
/// When available, efficiency values are gathered from the operating system. If
/// so, the [`DiscoverySupport::cpukind_efficiency()`] feature support flag
/// will be set. This is currently available on Windows 10, Mac OS X
/// (Darwin), and on some Linux platforms where core "capacity" is exposed in
/// sysfs. Efficiency values will range from 0 to the number of CPU kinds minus
/// one.
///
/// If the operating system does not expose core efficiencies natively, hwloc
/// tries to compute efficiencies by comparing CPU kinds using frequencies
/// (on ARM), or core types and frequencies (on other architectures). The
/// environment variable `HWLOC_CPUKINDS_RANKING` may be used to change this
/// heuristics, see [Environment
/// Variables](https://hwloc.readthedocs.io/en/v2.9/envvar.html).
///
/// If hwloc fails to rank any kind, for instance because the operating system
/// does not expose efficiencies and core frequencies, all kinds will have an
/// unknown efficiency (`None`), and they are not ordered in any specific way.
///
/// The kind that describes a given CPU set (if any, and not partially) may also
/// be queried with [`cpu_kind_from_set()`].
///
/// [`cpu_kind_from_set()`]: Topology::cpu_kind_from_set()
/// [`cpu_kinds()`]: Topology::cpu_kinds()
/// [`num_cpu_kinds()`]: Topology::num_cpu_kinds()
//
// --- Implementation details ---
//
// Upstream docs: https://hwloc.readthedocs.io/en/v2.9/group__hwlocality__cpukinds.html
impl Topology {
/// Number of different kinds of CPU cores in the topology
///
/// # Errors
///
/// - [`NoData`] if no information about CPU kinds was found
#[doc(alias = "hwloc_cpukinds_get_nr")]
pub fn num_cpu_kinds(&self) -> Result<NonZeroUsize, NoData> {
// SAFETY: - Topology is trusted to contain a valid ptr (type invariant)
// - hwloc ops are trusted not to modify *const parameters
// - Per documentation, flags should be zero
let count = errors::call_hwloc_int_normal("hwloc_cpukinds_get_nr", || unsafe {
hwlocality_sys::hwloc_cpukinds_get_nr(self.as_ptr(), 0)
})
.expect("All known failure cases are prevented by API design");
NonZeroUsize::new(int::expect_usize(count)).ok_or(NoData)
}
/// Enumerate CPU kinds, sorted by decreasing power-efficiency
///
/// The first listed CPU kind is most power-efficient, but has the weakest
/// peak performance. Subsequent CPU kinds will process computations faster,
/// but at the expense of consuming more power.
///
/// For each CPU kind, we provide the [`CpuSet`] of PUs belonging to that
/// kind, how efficient this CPU kind is (if CPU kind efficiencies are
/// known) and [other things we know about
/// it](https://hwloc.readthedocs.io/en/v2.9/topoattrs.html#topoattrs_cpukinds).
///
/// # Errors
///
/// - [`NoData`] if no information about CPU kinds was found
#[doc(alias = "hwloc_cpukinds_get_info")]
pub fn cpu_kinds(
&self,
) -> Result<
impl DoubleEndedIterator<Item = CpuKind<'_>> + Clone + ExactSizeIterator + FusedIterator,
NoData,
> {
// Iterate over all CPU kinds
let num_cpu_kinds = usize::from(self.num_cpu_kinds()?);
// SAFETY: This only calls cpu_kind() with valid kind_index values
Ok((0..num_cpu_kinds).map(move |kind_index| unsafe { self.cpu_kind(kind_index) }))
}
/// Tell what we know about a CPU kind
///
/// # Safety
///
/// This internal method should only be called on CPU kind indices which are
/// known to be valid by the high-level APIs.
unsafe fn cpu_kind(&self, kind_index: usize) -> CpuKind<'_> {
// Let hwloc tell us everything it knows about this CPU kind
let kind_index =
c_uint::try_from(kind_index).expect("Should not happen if API contract is honored");
let mut cpuset = CpuSet::new();
let mut efficiency = c_int::MIN;
let mut nr_infos: c_uint = 0;
let mut infos = ptr::null_mut();
// SAFETY: - Topology is trusted to contain a valid ptr (type invariant)
// - Bitmap is trusted to contain a valid ptr (type invariant)
// - hwloc ops are trusted not to modify *const parameters
// - hwloc ops are trusted to keep *mut parameters in a
// valid state unless stated otherwise
// - Per documentation, efficiency, nr_infos and infos are
// pure out parameters that hwloc does not read
// - Per documentation, flags should be zero
errors::call_hwloc_int_normal("hwloc_cpukinds_get_info", || unsafe {
hwlocality_sys::hwloc_cpukinds_get_info(
self.as_ptr(),
kind_index,
cpuset.as_mut_ptr(),
&mut efficiency,
&mut nr_infos,
&mut infos,
0,
)
})
.expect("All documented failure cases are prevented by API design");
// Post-process hwloc results, then emit them
let efficiency = match efficiency {
-1 => None,
other => {
let positive = c_uint::try_from(other).expect("Unexpected CpuEfficiency value");
Some(int::expect_usize(positive))
}
};
let infos = if infos.is_null() {
assert_eq!(
nr_infos, 0,
"hwloc pretended to yield {nr_infos} infos but provided a null infos pointer"
);
&[]
} else {
// SAFETY: - Per hwloc API contract, infos and nr_infos should be
// valid and point to valid state if the function returned
// successfully
// - We trust hwloc not to modify infos' target in a manner
// that violates Rust aliasing rules, as long as we honor
// these rules ourselves
// - Total size should not wrap for any valid allocation
// - AsNewtype is trusted to be implemented correctly
unsafe { std::slice::from_raw_parts(infos.as_newtype(), int::expect_usize(nr_infos)) }
};
CpuKind {
cpuset,
efficiency,
infos,
}
}
/// Query information about the CPU kind that contains CPUs listed in `set`
///
/// `set` can be a `&'_ CpuSet` or a `BitmapRef<'_, CpuSet>`.
///
/// # Errors
///
/// - [`PartiallyIncluded`] if `set` is only partially included in some kind
/// (i.e. some CPUs in the set belong to a kind, others to other kind(s))
/// - [`NotIncluded`] if `set` is not included in any kind, even partially
/// (i.e. CPU kind info isn't known or CPU set does not cover real CPUs)
///
/// [`NotIncluded`]: FromSetProblem::NotIncluded
/// [`PartiallyIncluded`]: FromSetProblem::PartiallyIncluded
#[doc(alias = "hwloc_cpukinds_get_by_cpuset")]
pub fn cpu_kind_from_set(
&self,
set: impl Deref<Target = CpuSet>,
) -> Result<CpuKind<'_>, FromSetError> {
/// Polymorphized version of this function (avoids generics code bloat)
fn polymorphized<'self_>(
self_: &'self_ Topology,
set: &CpuSet,
) -> Result<CpuKind<'self_>, FromSetError> {
// This reimplements hwloc_cpukinds_get_by_cpuset because it's very
// little code and doing it ourselves allows us to work around the
// pitfalls of relying on errno availability on Windows
let error = |problem| Err(FromSetError(set.clone(), problem));
match self_.cpu_kinds() {
Ok(kinds) => {
// Find relevant CPU kind, checking if unsuccessful matches
// are at least partial matches
let mut intersects = false;
for kind in kinds {
if kind.cpuset.includes(set) {
return Ok(kind);
} else if kind.cpuset.intersects(set) {
intersects = true;
}
}
// Report lack of matches accordingly
if intersects {
error(FromSetProblem::PartiallyIncluded)
} else {
error(FromSetProblem::NotIncluded)
}
}
Err(NoData) => error(FromSetProblem::NotIncluded),
}
}
polymorphized(self, &set)
}
}
/// Kind of CPU core
#[derive(Clone, Debug, Eq, Hash, PartialEq)]
pub struct CpuKind<'topology> {
/// CPUs that use this kind of core
pub cpuset: CpuSet,
/// CPU efficiency metric, if known
///
/// A lower metric value means that the CPU is expected to consume less
/// power, at the cost of possibly being less performant.
pub efficiency: Option<CpuEfficiency>,
/// Textual information
pub infos: &'topology [TextualInfo],
}
/// # Kinds of CPU cores
//
// --- Implementation details ---
//
// Upstream docs: https://hwloc.readthedocs.io/en/v2.9/group__hwlocality__cpukinds.html
impl TopologyEditor<'_> {
/// Register a kind of CPU in the topology.
///
/// Mark the PUs listed in `cpuset` as being of the same kind with respect
/// to the given attributes.
///
/// `cpuset` can be a `&'_ CpuSet` or a `BitmapRef<'_, CpuSet>`.
///
/// `forced_efficiency` should be `None` if unknown. Otherwise it is an
/// abstracted efficiency value to enforce the ranking of all kinds if all
/// of them have valid (and different) efficiencies.
///
/// Note that the efficiency reported later by [`Topology::cpu_kinds()`] may
/// differ because hwloc will scale efficiency values down to between 0 and
/// the number of kinds minus 1.
///
/// If `cpuset` overlaps with some existing kinds, those might get modified
/// or split. For instance if existing kind A contains PUs 0 and 1, and one
/// registers another kind for PU 1 and 2, there will be 3 resulting kinds:
/// existing kind A is restricted to only PU 0; new kind B contains only PU
/// 1 and combines information from A and from the newly-registered kind;
/// new kind C contains only PU 2 and only gets information from the
/// newly-registered kind.
///
/// # Errors
///
/// - [`ExcessiveEfficiency`] if `forced_efficiency` exceeds hwloc's
/// [`c_int::MAX`] limit.
/// - [`InfoContainsNul`] if a provided info's key or value contains NUL chars
/// - [`TooManyInfos`] if the number of specified (key, value) info tuples
/// exceeds hwloc's [`c_uint::MAX`] limit.
///
/// [`ExcessiveEfficiency`]: RegisterError::ExcessiveEfficiency
/// [`InfoContainsNul`]: RegisterError::InfoContainsNul
/// [`TooManyInfos`]: RegisterError::TooManyInfos
#[allow(clippy::collection_is_never_read)]
#[doc(alias = "hwloc_cpukinds_register")]
pub fn register_cpu_kind<'infos>(
&mut self,
cpuset: impl Deref<Target = CpuSet>,
forced_efficiency: Option<CpuEfficiency>,
infos: impl IntoIterator<Item = (&'infos str, &'infos str)>,
) -> Result<(), RegisterError> {
/// Polymorphized version of this function (avoids generics code bloat)
///
/// # Safety
///
/// The inner pointers of `raw_infos` must target valid NUL-terminated C
/// strings?
unsafe fn polymorphized(
self_: &mut TopologyEditor<'_>,
cpuset: &CpuSet,
forced_efficiency: Option<CpuEfficiency>,
raw_infos: Vec<hwloc_info_s>,
) -> Result<(), RegisterError> {
// Translate forced_efficiency into hwloc's preferred format
let forced_efficiency = if let Some(eff) = forced_efficiency {
c_int::try_from(eff).map_err(|_| RegisterError::ExcessiveEfficiency(eff))?
} else {
-1
};
// Translate number of infos into hwloc's preferred format
let infos_ptr = raw_infos.as_ptr();
let num_infos =
c_uint::try_from(raw_infos.len()).map_err(|_| RegisterError::TooManyInfos)?;
// SAFETY: - Topology is trusted to contain a valid ptr (type invariant)
// - Bitmap is trusted to contain a valid ptr (type invariant)
// - hwloc ops are trusted not to modify *const parameters
// - hwloc ops are trusted to keep *mut parameters in a
// valid state unless stated otherwise
// - Above logic enforces that forced_efficiency be >= -1,
// as hwloc demands
// - num_infos and infos_ptr originate from the same slice,
// so they should be valid and in sync
// - The source raw_infos struct has valid contents per
// function precondition
// - Per documentation, flags should be zero
errors::call_hwloc_int_normal("hwloc_cpukinds_register", || unsafe {
hwlocality_sys::hwloc_cpukinds_register(
self_.topology_mut_ptr(),
cpuset.as_ptr(),
forced_efficiency,
num_infos,
infos_ptr,
0,
)
})
.map(std::mem::drop)
.expect("All known failure cases are prevented by API design");
Ok(())
}
// Translate infos into hwloc's preferred format
let input_infos = infos.into_iter();
let mut infos = Vec::new();
let mut raw_infos = Vec::new();
if let Some(infos_len) = input_infos.size_hint().1 {
infos.reserve(infos_len);
raw_infos.reserve(infos_len);
}
for (name, value) in input_infos {
let new_string =
|s: &str| LibcString::new(s).map_err(|_| RegisterError::InfoContainsNul);
let (name, value) = (new_string(name)?, new_string(value)?);
// SAFETY: The source name and value LibcStrings are unmodified and
// retained by infos Vec until we're done using raw_infos
raw_infos.push(unsafe { TextualInfo::borrow_raw(&name, &value) });
infos.push((name, value));
}
// SAFETY: raw_infos contains valid infos (infos is still in scope,
// target strings have been checked for C suitability and
// converted to NUL-terminated format by LibcString)
unsafe { polymorphized(self, &cpuset, forced_efficiency, raw_infos) }
}
}
/// Efficiency of a CPU kind
///
/// A higher efficiency value means greater intrinsic performance (and possibly
/// less performance/power efficiency).
///
/// Efficiency ranges from 0 to the number of CPU kinds minus one.
pub type CpuEfficiency = usize;
/// No information about CPU kinds was found
///
/// The reason this is an error rather than a `None` option is that we know
/// there has to be at least one CPU kind in the system. hwloc just failed to
/// enumerate CPU kinds for some unknown reason.
#[derive(Copy, Clone, Debug, Default, Error, Eq, Hash, PartialEq)]
#[error("no information about CPU kinds was found")]
pub struct NoData;
/// Error while querying a CPU kind from a CPU set
#[derive(Clone, Debug, Error, Eq, Hash, PartialEq)]
#[error("CPU set {0} {1}")]
pub struct FromSetError(pub CpuSet, pub FromSetProblem);
/// Problem that was encountered while querying a CPU kind from a CPU set
//
// --- Implementation notes ---
//
// Not implementing Copy to leave room for future growth in case hwloc error
// semantics get clarified in a way that could use non-copy members someday.
#[allow(missing_copy_implementations)]
#[derive(Clone, Debug, Display, Eq, Hash, PartialEq)]
pub enum FromSetProblem {
/// CPU set is only partially included in some kind
///
/// i.e. some CPUs in the set belong to one kind, other CPUs belong to one
/// or more other kinds.
#[display("is only partially included in some CPU kind")]
PartiallyIncluded,
/// CPU set is not included in any kind, even partially
///
/// i.e. CPU kind info isn't known or this CPU set does not cover real CPUs.
#[display("isn't part of any known CPU kind")]
NotIncluded,
}
/// Error while registering a new CPU kind
#[derive(Copy, Clone, Debug, Error, Eq, Hash, PartialEq)]
pub enum RegisterError {
/// `forced_efficiency` value is above what hwloc can handle on this platform
#[error("CPU kind forced_efficiency value {0} is too high for hwloc")]
ExcessiveEfficiency(CpuEfficiency),
/// One of the CPU kind's textual info strings contains the NUL char
#[error("CPU kind textual info can't contain the NUL char")]
InfoContainsNul,
/// There are too many CPU kind textual info (key, value) pairs for hwloc
#[error("hwloc can't handle that much CPU kind textual info")]
TooManyInfos,
}
//
impl From<CpuEfficiency> for RegisterError {
fn from(value: CpuEfficiency) -> Self {
Self::ExcessiveEfficiency(value)
}
}