Scott Baker | 1fe7273 | 2019-10-21 10:58:51 -0700 | [diff] [blame] | 1 | // Copyright 2018 The Go Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | // CPU affinity functions |
| 6 | |
| 7 | package unix |
| 8 | |
| 9 | import ( |
| 10 | "unsafe" |
| 11 | ) |
| 12 | |
| 13 | const cpuSetSize = _CPU_SETSIZE / _NCPUBITS |
| 14 | |
| 15 | // CPUSet represents a CPU affinity mask. |
| 16 | type CPUSet [cpuSetSize]cpuMask |
| 17 | |
| 18 | func schedAffinity(trap uintptr, pid int, set *CPUSet) error { |
| 19 | _, _, e := RawSyscall(trap, uintptr(pid), uintptr(unsafe.Sizeof(*set)), uintptr(unsafe.Pointer(set))) |
| 20 | if e != 0 { |
| 21 | return errnoErr(e) |
| 22 | } |
| 23 | return nil |
| 24 | } |
| 25 | |
| 26 | // SchedGetaffinity gets the CPU affinity mask of the thread specified by pid. |
| 27 | // If pid is 0 the calling thread is used. |
| 28 | func SchedGetaffinity(pid int, set *CPUSet) error { |
| 29 | return schedAffinity(SYS_SCHED_GETAFFINITY, pid, set) |
| 30 | } |
| 31 | |
| 32 | // SchedSetaffinity sets the CPU affinity mask of the thread specified by pid. |
| 33 | // If pid is 0 the calling thread is used. |
| 34 | func SchedSetaffinity(pid int, set *CPUSet) error { |
| 35 | return schedAffinity(SYS_SCHED_SETAFFINITY, pid, set) |
| 36 | } |
| 37 | |
| 38 | // Zero clears the set s, so that it contains no CPUs. |
| 39 | func (s *CPUSet) Zero() { |
| 40 | for i := range s { |
| 41 | s[i] = 0 |
| 42 | } |
| 43 | } |
| 44 | |
| 45 | func cpuBitsIndex(cpu int) int { |
| 46 | return cpu / _NCPUBITS |
| 47 | } |
| 48 | |
| 49 | func cpuBitsMask(cpu int) cpuMask { |
| 50 | return cpuMask(1 << (uint(cpu) % _NCPUBITS)) |
| 51 | } |
| 52 | |
| 53 | // Set adds cpu to the set s. |
| 54 | func (s *CPUSet) Set(cpu int) { |
| 55 | i := cpuBitsIndex(cpu) |
| 56 | if i < len(s) { |
| 57 | s[i] |= cpuBitsMask(cpu) |
| 58 | } |
| 59 | } |
| 60 | |
| 61 | // Clear removes cpu from the set s. |
| 62 | func (s *CPUSet) Clear(cpu int) { |
| 63 | i := cpuBitsIndex(cpu) |
| 64 | if i < len(s) { |
| 65 | s[i] &^= cpuBitsMask(cpu) |
| 66 | } |
| 67 | } |
| 68 | |
| 69 | // IsSet reports whether cpu is in the set s. |
| 70 | func (s *CPUSet) IsSet(cpu int) bool { |
| 71 | i := cpuBitsIndex(cpu) |
| 72 | if i < len(s) { |
| 73 | return s[i]&cpuBitsMask(cpu) != 0 |
| 74 | } |
| 75 | return false |
| 76 | } |
| 77 | |
| 78 | // Count returns the number of CPUs in the set s. |
| 79 | func (s *CPUSet) Count() int { |
| 80 | c := 0 |
| 81 | for _, b := range s { |
| 82 | c += onesCount64(uint64(b)) |
| 83 | } |
| 84 | return c |
| 85 | } |
| 86 | |
| 87 | // onesCount64 is a copy of Go 1.9's math/bits.OnesCount64. |
| 88 | // Once this package can require Go 1.9, we can delete this |
| 89 | // and update the caller to use bits.OnesCount64. |
| 90 | func onesCount64(x uint64) int { |
| 91 | const m0 = 0x5555555555555555 // 01010101 ... |
| 92 | const m1 = 0x3333333333333333 // 00110011 ... |
| 93 | const m2 = 0x0f0f0f0f0f0f0f0f // 00001111 ... |
| 94 | const m3 = 0x00ff00ff00ff00ff // etc. |
| 95 | const m4 = 0x0000ffff0000ffff |
| 96 | |
| 97 | // Implementation: Parallel summing of adjacent bits. |
| 98 | // See "Hacker's Delight", Chap. 5: Counting Bits. |
| 99 | // The following pattern shows the general approach: |
| 100 | // |
| 101 | // x = x>>1&(m0&m) + x&(m0&m) |
| 102 | // x = x>>2&(m1&m) + x&(m1&m) |
| 103 | // x = x>>4&(m2&m) + x&(m2&m) |
| 104 | // x = x>>8&(m3&m) + x&(m3&m) |
| 105 | // x = x>>16&(m4&m) + x&(m4&m) |
| 106 | // x = x>>32&(m5&m) + x&(m5&m) |
| 107 | // return int(x) |
| 108 | // |
| 109 | // Masking (& operations) can be left away when there's no |
| 110 | // danger that a field's sum will carry over into the next |
| 111 | // field: Since the result cannot be > 64, 8 bits is enough |
| 112 | // and we can ignore the masks for the shifts by 8 and up. |
| 113 | // Per "Hacker's Delight", the first line can be simplified |
| 114 | // more, but it saves at best one instruction, so we leave |
| 115 | // it alone for clarity. |
| 116 | const m = 1<<64 - 1 |
| 117 | x = x>>1&(m0&m) + x&(m0&m) |
| 118 | x = x>>2&(m1&m) + x&(m1&m) |
| 119 | x = (x>>4 + x) & (m2 & m) |
| 120 | x += x >> 8 |
| 121 | x += x >> 16 |
| 122 | x += x >> 32 |
| 123 | return int(x) & (1<<7 - 1) |
| 124 | } |