affinity_linux.go

     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  	"math/bits"
    11  	"unsafe"
    12  )
    13  
    14  const cpuSetSize = _CPU_SETSIZE / _NCPUBITS
    15  
    16  // CPUSet represents a CPU affinity mask.
    17  type CPUSet [cpuSetSize]cpuMask
    18  
    19  func schedAffinity(trap uintptr, pid int, set *CPUSet) error {
    20  	_, _, e := RawSyscall(trap, uintptr(pid), uintptr(unsafe.Sizeof(*set)), uintptr(unsafe.Pointer(set)))
    21  	if e != 0 {
    22  		return errnoErr(e)
    23  	}
    24  	return nil
    25  }
    26  
    27  // SchedGetaffinity gets the CPU affinity mask of the thread specified by pid.
    28  // If pid is 0 the calling thread is used.
    29  func SchedGetaffinity(pid int, set *CPUSet) error {
    30  	return schedAffinity(SYS_SCHED_GETAFFINITY, pid, set)
    31  }
    32  
    33  // SchedSetaffinity sets the CPU affinity mask of the thread specified by pid.
    34  // If pid is 0 the calling thread is used.
    35  func SchedSetaffinity(pid int, set *CPUSet) error {
    36  	return schedAffinity(SYS_SCHED_SETAFFINITY, pid, set)
    37  }
    38  
    39  // Zero clears the set s, so that it contains no CPUs.
    40  func (s *CPUSet) Zero() {
    41  	clear(s[:])
    42  }
    43  
    44  // Fill adds all possible CPU bits to the set s. On Linux, [SchedSetaffinity]
    45  // will silently ignore any invalid CPU bits in [CPUSet] so this is an
    46  // efficient way of resetting the CPU affinity of a process.
    47  func (s *CPUSet) Fill() {
    48  	for i := range s {
    49  		s[i] = ^cpuMask(0)
    50  	}
    51  }
    52  
    53  func cpuBitsIndex(cpu int) int {
    54  	return cpu / _NCPUBITS
    55  }
    56  
    57  func cpuBitsMask(cpu int) cpuMask {
    58  	return cpuMask(1 << (uint(cpu) % _NCPUBITS))
    59  }
    60  
    61  // Set adds cpu to the set s.
    62  func (s *CPUSet) Set(cpu int) {
    63  	i := cpuBitsIndex(cpu)
    64  	if i < len(s) {
    65  		s[i] |= cpuBitsMask(cpu)
    66  	}
    67  }
    68  
    69  // Clear removes cpu from the set s.
    70  func (s *CPUSet) Clear(cpu int) {
    71  	i := cpuBitsIndex(cpu)
    72  	if i < len(s) {
    73  		s[i] &^= cpuBitsMask(cpu)
    74  	}
    75  }
    76  
    77  // IsSet reports whether cpu is in the set s.
    78  func (s *CPUSet) IsSet(cpu int) bool {
    79  	i := cpuBitsIndex(cpu)
    80  	if i < len(s) {
    81  		return s[i]&cpuBitsMask(cpu) != 0
    82  	}
    83  	return false
    84  }
    85  
    86  // Count returns the number of CPUs in the set s.
    87  func (s *CPUSet) Count() int {
    88  	c := 0
    89  	for _, b := range s {
    90  		c += bits.OnesCount64(uint64(b))
    91  	}
    92  	return c
    93  }
    94
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