scx_utils/
cpumask.rs

1// Copyright (c) Meta Platforms, Inc. and affiliates.
2
3// This software may be used and distributed according to the terms of the
4// GNU General Public License version 2.
5
6//! # SCX Cpumask
7//!
8//! A crate that allows creating, reading, and manipulating cpumasks.
9//!
10//! Cpumask
11//! -------
12//!
13//! A Cpumask object is simply a BitVec of u64's, along with a series of helper
14//! functions for creating, manipulating, and reading these BitVec objects.
15//!
16//! Empty Cpumasks can be created directly, or they can be created from a
17//! hexadecimal string:
18//!
19//!```no_run
20//!     use scx_utils::Cpumask;
21//!     let all_zeroes = Cpumask::new();
22//!     let from_str_mask = Cpumask::from_str("0xf0");
23//!```
24//!
25//! The hexadecimal string also supports the special values "none" and "all",
26//! respectively to specify no CPU (empty mask) or all CPUs (full mask):
27//!
28//!```
29//!     use scx_utils::Cpumask;
30//!     let str = String::from("none");
31//!     let all_zeroes = Cpumask::from_str(&str);
32//!
33//!     let str = String::from("all");
34//!     let all_ones = Cpumask::from_str(&str);
35//!```
36//!
37//! A Cpumask can be queried and updated using its helper functions:
38//!
39//!```rust
40//!     use log::info;
41//!     use scx_utils::Cpumask;
42//!     let str = String::from("none");
43//!     let mut mask = Cpumask::from_str(&str).unwrap();
44//!     info!("{:#?}", mask); // 32:<11111111000000001111111100000000>
45//!     assert!(!mask.test_cpu(0));
46//!     mask.set_cpu(0);
47//!     assert!(mask.test_cpu(0));
48//!
49//!     mask.clear_all();
50//!     info!("{:#?}", mask); // 32:<00000000000000000000000000000000>
51//!     assert!(!mask.test_cpu(0));
52//!
53//!     mask.set_all();
54//!     info!("{:#?}", mask); // 32:<11111111111111111111111111111111>
55//!     assert!(mask.test_cpu(0));
56//!```
57
58use crate::NR_CPU_IDS;
59use anyhow::bail;
60use anyhow::Context;
61use anyhow::Result;
62use bitvec::prelude::*;
63use sscanf::sscanf;
64use std::fmt;
65use std::ops::BitAndAssign;
66use std::ops::BitOrAssign;
67use std::ops::BitXorAssign;
68
69#[cfg(any(test, feature = "testutils"))]
70thread_local! {
71    /// Per-thread override for Cpumask width. 0 means use *NR_CPU_IDS.
72    /// Thread-local so parallel test threads don't interfere.
73    static MASK_WIDTH_OVERRIDE: std::cell::Cell<usize> = const { std::cell::Cell::new(0) };
74}
75
76/// Return the effective Cpumask width: the test override if set, else *NR_CPU_IDS.
77fn mask_width() -> usize {
78    #[cfg(any(test, feature = "testutils"))]
79    {
80        let ovr = MASK_WIDTH_OVERRIDE.with(|c| c.get());
81        if ovr > 0 {
82            return ovr;
83        }
84    }
85    *NR_CPU_IDS
86}
87
88/// Override the Cpumask width for the current thread. All subsequent
89/// Cpumask::new(), from_str(), and related calls on this thread will use
90/// this width instead of NR_CPU_IDS. Set to 0 to restore the default.
91#[cfg(any(test, feature = "testutils"))]
92pub fn set_cpumask_test_width(width: usize) {
93    MASK_WIDTH_OVERRIDE.with(|c| c.set(width));
94}
95
96#[derive(Debug, Eq, Clone, Hash, Ord, PartialEq, PartialOrd)]
97pub struct Cpumask {
98    mask: BitVec<u64, Lsb0>,
99}
100
101impl Cpumask {
102    fn check_cpu(&self, cpu: usize) -> Result<()> {
103        if cpu >= mask_width() {
104            bail!("Invalid CPU {} passed, max {}", cpu, mask_width());
105        }
106
107        Ok(())
108    }
109
110    /// Build a new empty Cpumask object.
111    pub fn new() -> Cpumask {
112        Cpumask {
113            mask: bitvec![u64, Lsb0; 0; mask_width()],
114        }
115    }
116
117    /// Build a Cpumask object from a hexadecimal string.
118    pub fn from_str(cpumask: &str) -> Result<Cpumask> {
119        match cpumask {
120            "none" => {
121                let mask = bitvec![u64, Lsb0; 0; mask_width()];
122                return Ok(Self { mask });
123            }
124            "all" => {
125                let mask = bitvec![u64, Lsb0; 1; mask_width()];
126                return Ok(Self { mask });
127            }
128            _ => {}
129        }
130        let hex_str = {
131            let mut tmp_str = cpumask
132                .strip_prefix("0x")
133                .unwrap_or(cpumask)
134                .replace('_', "");
135            if tmp_str.len() % 2 != 0 {
136                tmp_str = "0".to_string() + &tmp_str;
137            }
138            tmp_str
139        };
140        let byte_vec =
141            hex::decode(&hex_str).with_context(|| format!("Failed to parse cpumask: {cpumask}"))?;
142
143        let mut mask = bitvec![u64, Lsb0; 0; mask_width()];
144        for (index, &val) in byte_vec.iter().rev().enumerate() {
145            let mut v = val;
146            while v != 0 {
147                let lsb = v.trailing_zeros() as usize;
148                v &= !(1 << lsb);
149                let cpu = index * 8 + lsb;
150                if cpu >= mask_width() {
151                    bail!(
152                        concat!(
153                            "Found cpu ({}) in cpumask ({}) which is larger",
154                            " than the number of cpus on the machine ({})"
155                        ),
156                        cpu,
157                        cpumask,
158                        mask_width()
159                    );
160                }
161                mask.set(cpu, true);
162            }
163        }
164
165        Ok(Self { mask })
166    }
167
168    pub fn from_cpulist(cpulist: &str) -> Result<Cpumask> {
169        let mut mask = Cpumask::new();
170        for cpu_id in read_cpulist(cpulist)? {
171            let _ = mask.set_cpu(cpu_id);
172        }
173
174        Ok(mask)
175    }
176
177    /// Format the Cpumask as a compact CPU list string like "0-7,16-23".
178    /// Returns "none" if no CPUs are set.
179    pub fn to_cpulist(&self) -> String {
180        let cpus: Vec<usize> = self.iter().collect();
181        if cpus.is_empty() {
182            return String::from("none");
183        }
184
185        let mut ranges = Vec::new();
186        let mut start = cpus[0];
187        let mut end = cpus[0];
188
189        for &cpu in &cpus[1..] {
190            if cpu == end + 1 {
191                end = cpu;
192            } else {
193                ranges.push(if start == end {
194                    format!("{}", start)
195                } else {
196                    format!("{}-{}", start, end)
197                });
198                start = cpu;
199                end = cpu;
200            }
201        }
202
203        ranges.push(if start == end {
204            format!("{}", start)
205        } else {
206            format!("{}-{}", start, end)
207        });
208
209        ranges.join(",")
210    }
211
212    pub fn from_vec(vec: Vec<u64>) -> Self {
213        Self {
214            mask: BitVec::from_vec(vec),
215        }
216    }
217
218    pub fn from_bitvec(bitvec: BitVec<u64, Lsb0>) -> Self {
219        Self { mask: bitvec }
220    }
221
222    /// Return a slice of u64's whose bits reflect the Cpumask.
223    pub fn as_raw_slice(&self) -> &[u64] {
224        self.mask.as_raw_slice()
225    }
226
227    /// Return the mutable raw BitVec object backing the Cpumask.
228    pub fn as_raw_bitvec_mut(&mut self) -> &mut BitVec<u64, Lsb0> {
229        &mut self.mask
230    }
231
232    /// Return the raw BitVec object backing the Cpumask.
233    pub fn as_raw_bitvec(&self) -> &BitVec<u64, Lsb0> {
234        &self.mask
235    }
236
237    /// Set all bits in the Cpumask to 1
238    pub fn set_all(&mut self) {
239        self.mask.fill(true);
240    }
241
242    /// Set all bits in the Cpumask to 0
243    pub fn clear_all(&mut self) {
244        self.mask.fill(false);
245    }
246
247    /// Set a bit in the Cpumask. Returns an error if the specified CPU exceeds
248    /// the size of the Cpumask.
249    pub fn set_cpu(&mut self, cpu: usize) -> Result<()> {
250        self.check_cpu(cpu)?;
251        self.mask.set(cpu, true);
252        Ok(())
253    }
254
255    /// Clear a bit from the Cpumask. Returns an error if the specified CPU
256    /// exceeds the size of the Cpumask.
257    pub fn clear_cpu(&mut self, cpu: usize) -> Result<()> {
258        self.check_cpu(cpu)?;
259        self.mask.set(cpu, false);
260        Ok(())
261    }
262
263    /// Test whether the specified CPU bit is set in the Cpumask. If the CPU
264    /// exceeds the number of possible CPUs on the host, false is returned.
265    pub fn test_cpu(&self, cpu: usize) -> bool {
266        match self.mask.get(cpu) {
267            Some(bit) => *bit,
268            None => false,
269        }
270    }
271
272    /// Count the number of bits set in the Cpumask.
273    pub fn weight(&self) -> usize {
274        self.mask.count_ones()
275    }
276
277    /// Return true if the Cpumask has no bit set, false otherwise.
278    pub fn is_empty(&self) -> bool {
279        self.mask.count_ones() == 0
280    }
281
282    /// Return true if the Cpumask has all bits set, false otherwise.
283    pub fn is_full(&self) -> bool {
284        self.mask.count_ones() == mask_width()
285    }
286
287    /// The total size of the cpumask.
288    pub fn len(&self) -> usize {
289        mask_width()
290    }
291
292    /// Create a Cpumask that is the negation of the current Cpumask.
293    pub fn not(&self) -> Cpumask {
294        let mut new = self.clone();
295        new.mask = !new.mask;
296        new
297    }
298
299    /// Create a Cpumask that is the AND of the current Cpumask and another.
300    pub fn and(&self, other: &Cpumask) -> Cpumask {
301        let mut new = self.clone();
302        new.mask &= other.mask.clone();
303        new
304    }
305
306    /// Create a Cpumask that is the OR of the current Cpumask and another.
307    pub fn or(&self, other: &Cpumask) -> Cpumask {
308        let mut new = self.clone();
309        new.mask |= other.mask.clone();
310        new
311    }
312
313    /// Create a Cpumask that is the XOR of the current Cpumask and another.
314    pub fn xor(&self, other: &Cpumask) -> Cpumask {
315        let mut new = self.clone();
316        new.mask ^= other.mask.clone();
317        new
318    }
319
320    /// Iterate over each element of a Cpumask, and return the indices with bits
321    /// set.
322    ///
323    /// # Examples
324    ///
325    /// ```rust
326    /// use log::info;
327    /// use scx_utils::Cpumask;
328    /// let str = String::from("all");
329    /// let mask = Cpumask::from_str(&str).unwrap();
330    /// for cpu in mask.iter() {
331    ///     info!("cpu {} was set", cpu);
332    /// }
333    /// ```
334    pub fn iter(&self) -> CpumaskIterator<'_> {
335        CpumaskIterator {
336            mask: self,
337            index: 0,
338        }
339    }
340
341    /// Write out a CPU mask to a raw memory pointer. We normally use this as part of updating
342    /// the CPU masks on the BPF side.
343    ///
344    /// # Safety
345    ///
346    /// The caller must enforce that the bpfptr is valid and points to a valid region of
347    /// writable BPF memory that represents a CPU mask. This function is not thread safe.
348    pub unsafe fn write_to_ptr(&self, bpfptr: *mut u64, len: usize) -> Result<()> {
349        let cpumask_slice = self.as_raw_slice();
350        if len != cpumask_slice.len() {
351            bail!(
352                "BPF CPU mask has length {} u64s, Cpumask size is {}",
353                len,
354                cpumask_slice.len()
355            );
356        }
357
358        let ptr = bpfptr as *mut [u64; 64];
359        let bpfmask: &mut [u64; 64] = unsafe { &mut *ptr };
360        let (left, _) = bpfmask.split_at_mut(cpumask_slice.len());
361        left.clone_from_slice(cpumask_slice);
362
363        Ok(())
364    }
365
366    fn fmt_with(&self, f: &mut fmt::Formatter<'_>, case: char) -> fmt::Result {
367        let mut masks: Vec<u32> = self
368            .as_raw_slice()
369            .iter()
370            .flat_map(|x| [*x as u32, (x >> 32) as u32])
371            .collect();
372
373        // Throw out possible stray from u64 -> u32.
374        masks.truncate((mask_width()).div_ceil(32));
375
376        // Print the highest 32bit. Trim digits beyond mask_width().
377        let width = match (mask_width()).div_ceil(4) % 8 {
378            0 => 8,
379            v => v,
380        };
381        match case {
382            'x' => write!(f, "{:0width$x}", masks.pop().unwrap(), width = width)?,
383            'X' => write!(f, "{:0width$X}", masks.pop().unwrap(), width = width)?,
384            _ => unreachable!(),
385        }
386
387        // The rest in descending order.
388        for submask in masks.iter().rev() {
389            match case {
390                'x' => write!(f, ",{submask:08x}")?,
391                'X' => write!(f, ",{submask:08X}")?,
392                _ => unreachable!(),
393            }
394        }
395        Ok(())
396    }
397}
398
399pub fn read_cpulist(cpulist: &str) -> Result<Vec<usize>> {
400    let cpulist = cpulist.trim_end_matches('\0');
401    let cpu_groups: Vec<&str> = cpulist.split(',').collect();
402    let mut cpu_ids = vec![];
403    for group in cpu_groups.iter() {
404        let (min, max) = match sscanf!(group.trim(), "{usize}-{usize}") {
405            Some((x, y)) => (x, y),
406            None => match sscanf!(group.trim(), "{usize}") {
407                Some(x) => (x, x),
408                None => {
409                    bail!("Failed to parse cpulist {}", group.trim());
410                }
411            },
412        };
413        for i in min..(max + 1) {
414            cpu_ids.push(i);
415        }
416    }
417
418    Ok(cpu_ids)
419}
420
421pub struct CpumaskIterator<'a> {
422    mask: &'a Cpumask,
423    index: usize,
424}
425
426impl Iterator for CpumaskIterator<'_> {
427    type Item = usize;
428
429    fn next(&mut self) -> Option<Self::Item> {
430        while self.index < mask_width() {
431            let index = self.index;
432            self.index += 1;
433            let bit_val = self.mask.test_cpu(index);
434            if bit_val {
435                return Some(index);
436            }
437        }
438
439        None
440    }
441}
442
443impl fmt::Display for Cpumask {
444    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
445        self.fmt_with(f, 'x')
446    }
447}
448
449impl fmt::LowerHex for Cpumask {
450    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
451        self.fmt_with(f, 'x')
452    }
453}
454
455impl fmt::UpperHex for Cpumask {
456    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
457        self.fmt_with(f, 'X')
458    }
459}
460
461impl BitAndAssign<&Self> for Cpumask {
462    fn bitand_assign(&mut self, rhs: &Self) {
463        self.mask &= &rhs.mask;
464    }
465}
466
467impl BitOrAssign<&Self> for Cpumask {
468    fn bitor_assign(&mut self, rhs: &Self) {
469        self.mask |= &rhs.mask;
470    }
471}
472
473impl BitXorAssign<&Self> for Cpumask {
474    fn bitxor_assign(&mut self, rhs: &Self) {
475        self.mask ^= &rhs.mask;
476    }
477}
478
479#[cfg(test)]
480mod tests {
481    use super::*;
482
483    #[test]
484    fn test_to_cpulist_empty() {
485        let mask = Cpumask::new();
486        assert_eq!(mask.to_cpulist(), "none");
487    }
488
489    #[test]
490    fn test_to_cpulist_single_cpu() {
491        set_cpumask_test_width(16);
492        let mut mask = Cpumask::new();
493        mask.set_cpu(5).unwrap();
494        assert_eq!(mask.to_cpulist(), "5");
495    }
496
497    #[test]
498    fn test_to_cpulist_contiguous_range() {
499        set_cpumask_test_width(16);
500        let mut mask = Cpumask::new();
501        for cpu in 0..8 {
502            mask.set_cpu(cpu).unwrap();
503        }
504        assert_eq!(mask.to_cpulist(), "0-7");
505    }
506
507    #[test]
508    fn test_to_cpulist_multiple_ranges() {
509        set_cpumask_test_width(16);
510        let mut mask = Cpumask::new();
511        for cpu in 0..4 {
512            mask.set_cpu(cpu).unwrap();
513        }
514        for cpu in 8..12 {
515            mask.set_cpu(cpu).unwrap();
516        }
517        assert_eq!(mask.to_cpulist(), "0-3,8-11");
518    }
519
520    #[test]
521    fn test_to_cpulist_scattered() {
522        set_cpumask_test_width(16);
523        let mut mask = Cpumask::new();
524        mask.set_cpu(1).unwrap();
525        mask.set_cpu(3).unwrap();
526        mask.set_cpu(5).unwrap();
527        assert_eq!(mask.to_cpulist(), "1,3,5");
528    }
529
530    #[test]
531    fn test_to_cpulist_mixed() {
532        set_cpumask_test_width(16);
533        let mut mask = Cpumask::new();
534        mask.set_cpu(0).unwrap();
535        mask.set_cpu(1).unwrap();
536        mask.set_cpu(2).unwrap();
537        mask.set_cpu(5).unwrap();
538        mask.set_cpu(10).unwrap();
539        mask.set_cpu(11).unwrap();
540        assert_eq!(mask.to_cpulist(), "0-2,5,10-11");
541    }
542
543    #[test]
544    fn test_to_cpulist_roundtrip() {
545        set_cpumask_test_width(32);
546        let original = "0-3,8-11,16";
547        let mask = Cpumask::from_cpulist(original).unwrap();
548        assert_eq!(mask.to_cpulist(), original);
549    }
550}
scx_utils/cpumask.rs

scx_utils/
cpumask.rs
