129 lines
3.3 KiB
Go
129 lines
3.3 KiB
Go
// Copyright 2018 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// CPU affinity functions
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package unix
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import (
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"unsafe"
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)
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const cpuSetSize = _CPU_SETSIZE / _NCPUBITS
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// CPUSet represents a CPU affinity mask.
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type CPUSet [cpuSetSize]cpuMask
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func schedAffinity(trap uintptr, pid int, set *CPUSet) error {
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_, _, e := RawSyscall(trap, uintptr(pid), uintptr(unsafe.Sizeof(*set)), uintptr(unsafe.Pointer(set)))
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if e != 0 {
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return errnoErr(e)
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}
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return nil
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}
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// SchedGetaffinity gets the CPU affinity mask of the thread specified by pid.
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// If pid is 0 the calling thread is used.
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func SchedGetaffinity(pid int, set *CPUSet) error {
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return schedAffinity(SYS_SCHED_GETAFFINITY, pid, set)
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}
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// SchedSetaffinity sets the CPU affinity mask of the thread specified by pid.
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// If pid is 0 the calling thread is used.
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func SchedSetaffinity(pid int, set *CPUSet) error {
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return schedAffinity(SYS_SCHED_SETAFFINITY, pid, set)
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}
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// Zero clears the set s, so that it contains no CPUs.
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func (s *CPUSet) Zero() {
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for i := range s {
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s[i] = 0
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}
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}
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func cpuBitsIndex(cpu int) int {
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return cpu / _NCPUBITS
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}
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func cpuBitsMask(cpu int) cpuMask {
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return cpuMask(1 << (uint(cpu) % _NCPUBITS))
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}
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// Set adds cpu to the set s.
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func (s *CPUSet) Set(cpu int) {
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i := cpuBitsIndex(cpu)
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if i < len(s) {
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s[i] |= cpuBitsMask(cpu)
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}
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}
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// Clear removes cpu from the set s.
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func (s *CPUSet) Clear(cpu int) {
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i := cpuBitsIndex(cpu)
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if i < len(s) {
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s[i] &^= cpuBitsMask(cpu)
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}
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}
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// IsSet reports whether cpu is in the set s.
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func (s *CPUSet) IsSet(cpu int) bool {
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i := cpuBitsIndex(cpu)
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if i < len(s) {
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return s[i]&cpuBitsMask(cpu) != 0
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}
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return false
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}
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// Count returns the number of CPUs in the set s.
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func (s *CPUSet) Count() int {
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c := 0
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for _, b := range s {
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c += onesCount64(uint64(b))
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}
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return c
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}
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// onesCount64 is a copy of Go 1.9's math/bits.OnesCount64.
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// Once this package can require Go 1.9, we can delete this
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// and update the caller to use bits.OnesCount64.
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func onesCount64(x uint64) int {
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const m0 = 0x5555555555555555 // 01010101 ...
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const m1 = 0x3333333333333333 // 00110011 ...
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const m2 = 0x0f0f0f0f0f0f0f0f // 00001111 ...
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// Unused in this function, but definitions preserved for
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// documentation purposes:
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//
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// const m3 = 0x00ff00ff00ff00ff // etc.
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// const m4 = 0x0000ffff0000ffff
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//
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// Implementation: Parallel summing of adjacent bits.
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// See "Hacker's Delight", Chap. 5: Counting Bits.
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// The following pattern shows the general approach:
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//
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// x = x>>1&(m0&m) + x&(m0&m)
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// x = x>>2&(m1&m) + x&(m1&m)
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// x = x>>4&(m2&m) + x&(m2&m)
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// x = x>>8&(m3&m) + x&(m3&m)
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// x = x>>16&(m4&m) + x&(m4&m)
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// x = x>>32&(m5&m) + x&(m5&m)
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// return int(x)
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//
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// Masking (& operations) can be left away when there's no
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// danger that a field's sum will carry over into the next
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// field: Since the result cannot be > 64, 8 bits is enough
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// and we can ignore the masks for the shifts by 8 and up.
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// Per "Hacker's Delight", the first line can be simplified
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// more, but it saves at best one instruction, so we leave
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// it alone for clarity.
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const m = 1<<64 - 1
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x = x>>1&(m0&m) + x&(m0&m)
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x = x>>2&(m1&m) + x&(m1&m)
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x = (x>>4 + x) & (m2 & m)
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x += x >> 8
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x += x >> 16
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x += x >> 32
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return int(x) & (1<<7 - 1)
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}
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