]>
Commit | Line | Data |
---|---|---|
15c0b25d AP |
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 | } |