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// Copyright 2018 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package sched
import "math/bits"
const (
bitsPerByte = 8
bytesPerLong = 8 // only for 64-bit architectures
)
// CPUSet contains a bitmap to record CPU information.
//
// Note that this definition is only correct for little-endian architectures,
// since Linux's cpumask_t uses unsigned long.
type CPUSet []byte
// CPUSetSize returns the size in bytes of a CPUSet that can contain num cpus.
func CPUSetSize(num uint) uint {
// NOTE(b/68859821): Applications may expect that the size of a CPUSet in
// bytes is always a multiple of sizeof(unsigned long), since this is true
// in Linux. Thus we always round up.
bytes := (num + bitsPerByte - 1) / bitsPerByte
longs := (bytes + bytesPerLong - 1) / bytesPerLong
return longs * bytesPerLong
}
// NewCPUSet returns a CPUSet for the given number of CPUs which initially
// contains no CPUs.
func NewCPUSet(num uint) CPUSet {
return CPUSet(make([]byte, CPUSetSize(num)))
}
// NewFullCPUSet returns a CPUSet for the given number of CPUs, all of which
// are present in the set.
func NewFullCPUSet(num uint) CPUSet {
c := NewCPUSet(num)
var i uint
for ; i < num/bitsPerByte; i++ {
c[i] = 0xff
}
if rem := num % bitsPerByte; rem != 0 {
c[i] = (1 << rem) - 1
}
return c
}
// Size returns the size of 'c' in bytes.
func (c CPUSet) Size() uint {
return uint(len(c))
}
// NumCPUs returns how many cpus are set in the CPUSet.
func (c CPUSet) NumCPUs() uint {
var n int
for _, b := range c {
n += bits.OnesCount8(b)
}
return uint(n)
}
// Copy returns a copy of the CPUSet.
func (c CPUSet) Copy() CPUSet {
return append(CPUSet(nil), c...)
}
// Set sets the bit corresponding to cpu.
func (c *CPUSet) Set(cpu uint) {
(*c)[cpu/bitsPerByte] |= 1 << (cpu % bitsPerByte)
}
// ClearAbove clears bits corresponding to cpu and all higher cpus.
func (c *CPUSet) ClearAbove(cpu uint) {
i := cpu / bitsPerByte
if i >= c.Size() {
return
}
(*c)[i] &^= 0xff << (cpu % bitsPerByte)
for i++; i < c.Size(); i++ {
(*c)[i] = 0
}
}
// ForEachCPU iterates over the CPUSet and calls fn with the cpu index if
// it's set.
func (c CPUSet) ForEachCPU(fn func(uint)) {
for i := uint(0); i < c.Size()*bitsPerByte; i++ {
bit := uint(1) << (i & (bitsPerByte - 1))
if uint(c[i/bitsPerByte])&bit == bit {
fn(i)
}
}
}
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