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1 // Copyright 2018 The Go Authors. All rights reserved.
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2 // Use of this source code is governed by a BSD-style
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3 // license that can be found in the LICENSE file.
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4
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5 // CPU affinity functions
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6
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7 package unix
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8
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9 import (
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10 "math/bits"
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11 "unsafe"
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12 )
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13
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14 const cpuSetSize = _CPU_SETSIZE / _NCPUBITS
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15
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16 // CPUSet represents a CPU affinity mask.
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17 type CPUSet [cpuSetSize]cpuMask
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18
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19 func schedAffinity(trap uintptr, pid int, set *CPUSet) error {
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20 _, _, e := RawSyscall(trap, uintptr(pid), uintptr(unsafe.Sizeof(*set)), uintptr(unsafe.Pointer(set)))
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21 if e != 0 {
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22 return errnoErr(e)
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23 }
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24 return nil
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25 }
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26
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27 // SchedGetaffinity gets the CPU affinity mask of the thread specified by pid.
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28 // If pid is 0 the calling thread is used.
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29 func SchedGetaffinity(pid int, set *CPUSet) error {
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30 return schedAffinity(SYS_SCHED_GETAFFINITY, pid, set)
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31 }
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32
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33 // SchedSetaffinity sets the CPU affinity mask of the thread specified by pid.
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34 // If pid is 0 the calling thread is used.
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35 func SchedSetaffinity(pid int, set *CPUSet) error {
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36 return schedAffinity(SYS_SCHED_SETAFFINITY, pid, set)
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37 }
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38
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39 // Zero clears the set s, so that it contains no CPUs.
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40 func (s *CPUSet) Zero() {
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41 for i := range s {
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42 s[i] = 0
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43 }
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44 }
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45
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46 func cpuBitsIndex(cpu int) int {
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47 return cpu / _NCPUBITS
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48 }
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49
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50 func cpuBitsMask(cpu int) cpuMask {
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51 return cpuMask(1 << (uint(cpu) % _NCPUBITS))
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52 }
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53
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54 // Set adds cpu to the set s.
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55 func (s *CPUSet) Set(cpu int) {
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56 i := cpuBitsIndex(cpu)
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57 if i < len(s) {
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58 s[i] |= cpuBitsMask(cpu)
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59 }
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60 }
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61
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62 // Clear removes cpu from the set s.
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63 func (s *CPUSet) Clear(cpu int) {
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64 i := cpuBitsIndex(cpu)
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65 if i < len(s) {
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66 s[i] &^= cpuBitsMask(cpu)
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67 }
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68 }
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69
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70 // IsSet reports whether cpu is in the set s.
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71 func (s *CPUSet) IsSet(cpu int) bool {
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72 i := cpuBitsIndex(cpu)
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73 if i < len(s) {
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74 return s[i]&cpuBitsMask(cpu) != 0
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75 }
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76 return false
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77 }
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78
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79 // Count returns the number of CPUs in the set s.
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80 func (s *CPUSet) Count() int {
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81 c := 0
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82 for _, b := range s {
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83 c += bits.OnesCount64(uint64(b))
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84 }
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85 return c
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86 }
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