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