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| 1 | +// Copyright 2024 The NativeLink Authors. All rights reserved. |
| 2 | +// |
| 3 | +// Licensed under the Functional Source License, Version 1.1, Apache 2.0 Future License (the "License"); |
| 4 | +// you may not use this file except in compliance with the License. |
| 5 | +// You may obtain a copy of the License at |
| 6 | +// |
| 7 | +// See LICENSE file for details |
| 8 | +// |
| 9 | +// Unless required by applicable law or agreed to in writing, software |
| 10 | +// distributed under the License is distributed on an "AS IS" BASIS, |
| 11 | +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 12 | +// See the License for the specific language governing permissions and |
| 13 | +// limitations under the License. |
| 14 | + |
| 15 | +//! Darwin `QoS` (Quality of Service) helpers for worker scheduling. |
| 16 | +//! |
| 17 | +//! Apple Silicon (M-series) CPUs have a heterogeneous topology with |
| 18 | +//! performance ("P") and efficiency ("E") cores. XNU's scheduler routes |
| 19 | +//! threads to P or E cores in part based on the thread's `QoS` class. The |
| 20 | +//! default class assigned to long-running background daemons is typically |
| 21 | +//! `UTILITY` or `BACKGROUND`, both of which the scheduler may park on |
| 22 | +//! E-cores. |
| 23 | +//! |
| 24 | +//! Single-thread-bursty workloads such as `swift-frontend` and `clang` |
| 25 | +//! invocations (typical in iOS RBE builds) can run 2x–3x slower when |
| 26 | +//! pinned to an E-core. Tagging the worker process with |
| 27 | +//! `QOS_CLASS_USER_INITIATED` tells the scheduler to treat its threads |
| 28 | +//! as foreground-equivalent and bias placement toward P-cores. |
| 29 | +//! |
| 30 | +//! On Linux and Windows these helpers compile away to nothing — they are |
| 31 | +//! intentionally not behind a runtime branch so non-macOS builds never |
| 32 | +//! emit a call. |
| 33 | +
|
| 34 | +/// Sets the calling thread's `QoS` class to `USER_INITIATED` on macOS. |
| 35 | +/// |
| 36 | +/// Returns `true` if the underlying `pthread_set_qos_class_self_np` |
| 37 | +/// call succeeded; returns `false` if it failed. |
| 38 | +/// |
| 39 | +/// Safe to call from any thread, including tokio runtime worker threads |
| 40 | +/// via `Builder::on_thread_start`. |
| 41 | +#[cfg(target_os = "macos")] |
| 42 | +#[inline] |
| 43 | +pub fn set_user_initiated() -> bool { |
| 44 | + // SAFETY: `pthread_set_qos_class_self_np` is a thread-local |
| 45 | + // setter with no preconditions on the caller; passing a valid |
| 46 | + // enum variant and relative priority 0 is always defined. |
| 47 | + let ret = unsafe { |
| 48 | + libc::pthread_set_qos_class_self_np(libc::qos_class_t::QOS_CLASS_USER_INITIATED, 0) |
| 49 | + }; |
| 50 | + ret == 0 |
| 51 | +} |
| 52 | + |
| 53 | +/// Compile-time no-op on non-macOS targets. |
| 54 | +/// |
| 55 | +/// Always returns `true`. The call site expands to nothing after |
| 56 | +/// inlining / dead-code elimination, so non-macOS builds never emit |
| 57 | +/// a runtime branch or a libc call. |
| 58 | +#[cfg(not(target_os = "macos"))] |
| 59 | +#[inline] |
| 60 | +pub const fn set_user_initiated() -> bool { |
| 61 | + true |
| 62 | +} |
| 63 | + |
| 64 | +#[cfg(all(test, target_os = "macos"))] |
| 65 | +mod macos_tests { |
| 66 | + use super::set_user_initiated; |
| 67 | + |
| 68 | + /// Reads the current thread's `QoS` class via `pthread_get_qos_class_np`. |
| 69 | + /// Panics with a contextual message on failure (only called from tests). |
| 70 | + fn current_qos_class() -> libc::qos_class_t { |
| 71 | + let mut class: libc::qos_class_t = libc::qos_class_t::QOS_CLASS_UNSPECIFIED; |
| 72 | + let mut rel_prio: libc::c_int = 0; |
| 73 | + // SAFETY: out-pointers point to stack-allocated, properly sized |
| 74 | + // and aligned storage owned by this thread. |
| 75 | + let ret = unsafe { |
| 76 | + libc::pthread_get_qos_class_np( |
| 77 | + libc::pthread_self(), |
| 78 | + core::ptr::from_mut(&mut class), |
| 79 | + core::ptr::from_mut(&mut rel_prio), |
| 80 | + ) |
| 81 | + }; |
| 82 | + assert_eq!(ret, 0, "pthread_get_qos_class_np failed: {ret}"); |
| 83 | + class |
| 84 | + } |
| 85 | + |
| 86 | + /// Proves the `QoS` call is wired up on macOS and the underlying |
| 87 | + /// Darwin symbol resolves at link time. A failure here means the |
| 88 | + /// worker would silently keep running on E-cores. |
| 89 | + #[test] |
| 90 | + fn sets_user_initiated_on_current_thread() { |
| 91 | + assert!( |
| 92 | + set_user_initiated(), |
| 93 | + "pthread_set_qos_class_self_np(USER_INITIATED) returned non-zero", |
| 94 | + ); |
| 95 | + // `qos_class_t` is a `#[repr(u32)]` C enum that does not derive |
| 96 | + // `PartialEq` in libc, so compare the underlying discriminants. |
| 97 | + assert_eq!( |
| 98 | + current_qos_class() as u32, |
| 99 | + libc::qos_class_t::QOS_CLASS_USER_INITIATED as u32, |
| 100 | + "`QoS` class did not update; thread will be eligible for E-core scheduling", |
| 101 | + ); |
| 102 | + } |
| 103 | + |
| 104 | + /// Validates the load-bearing claim that tokio worker threads created |
| 105 | + /// with a `Builder::on_thread_start` hook calling `set_user_initiated` |
| 106 | + /// observe `QOS_CLASS_USER_INITIATED` from inside spawned tasks. This |
| 107 | + /// mirrors the wiring in `src/bin/nativelink.rs::main`. Without this |
| 108 | + /// test the entire `QoS` scheme is unverified at the integration level. |
| 109 | + /// |
| 110 | + /// This is the one place in the worker crate that must construct a |
| 111 | + /// fresh `tokio::runtime::Builder::new_multi_thread()` and drive it |
| 112 | + /// with `block_on` — the unit under test *is* the `on_thread_start` |
| 113 | + /// hook on a custom-built runtime, which `nativelink-util::task` and |
| 114 | + /// `#[nativelink_test]` do not expose. The `#[expect]` mirrors the |
| 115 | + /// same justified escape used in `src/bin/nativelink.rs::main`. |
| 116 | + #[test] |
| 117 | + #[expect( |
| 118 | + clippy::disallowed_methods, |
| 119 | + reason = "test exercises `Builder::on_thread_start` + `block_on`; \ |
| 120 | + no util wrapper exposes a custom-built runtime with a thread-start hook" |
| 121 | + )] |
| 122 | + fn tokio_worker_threads_inherit_user_initiated_via_on_thread_start() { |
| 123 | + // Deliberately build a fresh runtime in-test (do not reuse a |
| 124 | + // global one) so the hook is exercised on freshly-spawned |
| 125 | + // worker threads with whatever class they were born with. |
| 126 | + let rt = tokio::runtime::Builder::new_multi_thread() |
| 127 | + .worker_threads(2) |
| 128 | + .on_thread_start(|| { |
| 129 | + assert!(set_user_initiated(), "hook failed in worker thread"); |
| 130 | + }) |
| 131 | + .enable_all() |
| 132 | + .build() |
| 133 | + .expect("build tokio runtime"); |
| 134 | + |
| 135 | + let observed: u32 = rt.block_on(async { |
| 136 | + // Force execution on a worker thread (not the caller). |
| 137 | + tokio::spawn(async { current_qos_class() as u32 }) |
| 138 | + .await |
| 139 | + .expect("join spawned task") |
| 140 | + }); |
| 141 | + |
| 142 | + assert_eq!( |
| 143 | + observed, |
| 144 | + libc::qos_class_t::QOS_CLASS_USER_INITIATED as u32, |
| 145 | + "tokio worker thread did not inherit USER_INITIATED from on_thread_start", |
| 146 | + ); |
| 147 | + } |
| 148 | +} |
| 149 | + |
| 150 | +#[cfg(all(test, not(target_os = "macos")))] |
| 151 | +mod non_macos_tests { |
| 152 | + use super::set_user_initiated; |
| 153 | + |
| 154 | + /// On Linux/Windows the function must be a true no-op that always |
| 155 | + /// reports success — there is no runtime cost and no platform call. |
| 156 | + #[test] |
| 157 | + fn is_a_noop_on_non_macos() { |
| 158 | + assert!(set_user_initiated()); |
| 159 | + } |
| 160 | +} |
| 161 | + |
| 162 | +/// Compile-time assertion: when `target_os` is not `macos`, this module |
| 163 | +/// must not reference any libc symbol. Reviewers can `grep "extern crate |
| 164 | +/// libc"` or inspect this constant to verify the no-op story. |
| 165 | +#[cfg(not(target_os = "macos"))] |
| 166 | +pub const NON_MACOS_IS_NOOP: () = (); |
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