unix: add SchedGetaffinity and SchedSetaffinity on Linux

SchedGetaffinity and SchedSetaffinity are used to get and set a thread's
CPU affinity mask.

See http://man7.org/linux/man-pages/man2/sched_setaffinity.2.html for
details.

Also add a manual implementation of CpuSet_t and the corresponding
accessor functions (mimicking the CPU_* macros from sched.h).

Fixes golang/go#11243

Change-Id: Ia5abc0053cd06810b3b09ab65c27434f5323c1ad
Reviewed-on: https://go-review.googlesource.com/85915
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/affinity_linux.go

+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// CPU affinity functions
+
+package unix
+
+import (
+	"math/bits"
+	"unsafe"
+)
+
+const cpuSetSize = _CPU_SETSIZE / _NCPUBITS
+
+// CPUSet represents a CPU affinity mask.
+type CPUSet [cpuSetSize]cpuMask
+
+func schedAffinity(trap uintptr, pid int, set *CPUSet) error {
+	_, _, e := RawSyscall(trap, uintptr(pid), uintptr(unsafe.Sizeof(set)), uintptr(unsafe.Pointer(set)))
+	if e != 0 {
+		return errnoErr(e)
+	}
+	return nil
+}
+
+// SchedGetaffinity gets the CPU affinity mask of the thread specified by pid.
+// If pid is 0 the calling thread is used.
+func SchedGetaffinity(pid int, set *CPUSet) error {
+	return schedAffinity(SYS_SCHED_GETAFFINITY, pid, set)
+}
+
+// SchedSetaffinity sets the CPU affinity mask of the thread specified by pid.
+// If pid is 0 the calling thread is used.
+func SchedSetaffinity(pid int, set *CPUSet) error {
+	return schedAffinity(SYS_SCHED_SETAFFINITY, pid, set)
+}
+
+// Zero clears the set s, so that it contains no CPUs.
+func (s *CPUSet) Zero() {
+	for i := range s {
+		s[i] = 0
+	}
+}
+
+func cpuBitsIndex(cpu int) int {
+	return cpu / _NCPUBITS
+}
+
+func cpuBitsMask(cpu int) cpuMask {
+	return cpuMask(1 << (uint(cpu) % _NCPUBITS))
+}
+
+// Set adds cpu to the set s.
+func (s *CPUSet) Set(cpu int) {
+	i := cpuBitsIndex(cpu)
+	if i < len(s) {
+		s[i] |= cpuBitsMask(cpu)
+	}
+}
+
+// Clear removes cpu from the set s.
+func (s *CPUSet) Clear(cpu int) {
+	i := cpuBitsIndex(cpu)
+	if i < len(s) {
+		s[i] &^= cpuBitsMask(cpu)
+	}
+}
+
+// IsSet reports whether cpu is in the set s.
+func (s *CPUSet) IsSet(cpu int) bool {
+	i := cpuBitsIndex(cpu)
+	if i < len(s) {
+		return s[i]&cpuBitsMask(cpu) != 0
+	}
+	return false
+}
+
+// Count returns the number of CPUs in the set s.
+func (s *CPUSet) Count() int {
+	c := 0
+	for _, b := range s {
+		c += bits.OnesCount64(uint64(b))
+	}
+	return c
+}

unix/linux/types.go

@@ -24,6 +24,7 @@ package unix
 #include <netinet/tcp.h>
 #include <netpacket/packet.h>
 #include <poll.h>
+#include <sched.h>
 #include <signal.h>
 #include <stdio.h>
 #include <sys/epoll.h>
@@ -594,3 +595,12 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = C.CTRL_ATTR_MCAST_GRP_NAME
 	CTRL_ATTR_MCAST_GRP_ID     = C.CTRL_ATTR_MCAST_GRP_ID
 )
+
+// CPU affinity
+
+type cpuMask C.__cpu_mask
+
+const (
+	_CPU_SETSIZE = C.__CPU_SETSIZE
+	_NCPUBITS    = C.__NCPUBITS
+)

unix/syscall_linux.go

@@ -1455,11 +1455,9 @@ func Vmsplice(fd int, iovs []Iovec, flags int) (int, error) {
 // RtSigtimedwait
 // SchedGetPriorityMax
 // SchedGetPriorityMin
-// SchedGetaffinity
 // SchedGetparam
 // SchedGetscheduler
 // SchedRrGetInterval
-// SchedSetaffinity
 // SchedSetparam
 // SchedYield
 // Security

unix/syscall_linux_test.go

@@ -9,6 +9,7 @@ package unix_test
 import (
 	"io/ioutil"
 	"os"
+	"runtime"
 	"testing"
 	"time"
 
@@ -255,6 +256,58 @@ func TestFstatat(t *testing.T) {
 	}
 }
 
+func TestSchedSetaffinity(t *testing.T) {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	var oldMask unix.CPUSet
+	err := unix.SchedGetaffinity(0, &oldMask)
+	if err != nil {
+		t.Fatalf("SchedGetaffinity: %v", err)
+	}
+
+	var newMask unix.CPUSet
+	newMask.Zero()
+	if newMask.Count() != 0 {
+		t.Errorf("CpuZero: didn't zero CPU set: %v", newMask)
+	}
+	cpu := 1
+	newMask.Set(cpu)
+	if newMask.Count() != 1 || !newMask.IsSet(cpu) {
+		t.Errorf("CpuSet: didn't set CPU %d in set: %v", cpu, newMask)
+	}
+	cpu = 5
+	newMask.Set(cpu)
+	if newMask.Count() != 2 || !newMask.IsSet(cpu) {
+		t.Errorf("CpuSet: didn't set CPU %d in set: %v", cpu, newMask)
+	}
+	newMask.Clear(cpu)
+	if newMask.Count() != 1 || newMask.IsSet(cpu) {
+		t.Errorf("CpuClr: didn't clear CPU %d in set: %v", cpu, newMask)
+	}
+
+	err = unix.SchedSetaffinity(0, &newMask)
+	if err != nil {
+		t.Fatalf("SchedSetaffinity: %v", err)
+	}
+
+	var gotMask unix.CPUSet
+	err = unix.SchedGetaffinity(0, &gotMask)
+	if err != nil {
+		t.Fatalf("SchedGetaffinity: %v", err)
+	}
+
+	if gotMask != newMask {
+		t.Errorf("SchedSetaffinity: returned affinity mask does not match set affinity mask")
+	}
+
+	// Restore old mask so it doesn't affect successive tests
+	err = unix.SchedSetaffinity(0, &oldMask)
+	if err != nil {
+		t.Fatalf("SchedSetaffinity: %v", err)
+	}
+}
+
 // utilities taken from os/os_test.go
 
 func touch(t *testing.T, name string) {

unix/ztypes_linux_386.go

@@ -792,3 +792,10 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = 0x1
 	CTRL_ATTR_MCAST_GRP_ID     = 0x2
 )
+
+type cpuMask uint32
+
+const (
+	_CPU_SETSIZE = 0x400
+	_NCPUBITS    = 0x20
+)

unix/ztypes_linux_amd64.go

@@ -810,3 +810,10 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = 0x1
 	CTRL_ATTR_MCAST_GRP_ID     = 0x2
 )
+
+type cpuMask uint64
+
+const (
+	_CPU_SETSIZE = 0x400
+	_NCPUBITS    = 0x40
+)

unix/ztypes_linux_arm.go

@@ -781,3 +781,10 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = 0x1
 	CTRL_ATTR_MCAST_GRP_ID     = 0x2
 )
+
+type cpuMask uint32
+
+const (
+	_CPU_SETSIZE = 0x400
+	_NCPUBITS    = 0x20
+)

unix/ztypes_linux_arm64.go

@@ -789,3 +789,10 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = 0x1
 	CTRL_ATTR_MCAST_GRP_ID     = 0x2
 )
+
+type cpuMask uint64
+
+const (
+	_CPU_SETSIZE = 0x400
+	_NCPUBITS    = 0x40
+)

unix/ztypes_linux_mips.go

@@ -786,3 +786,10 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = 0x1
 	CTRL_ATTR_MCAST_GRP_ID     = 0x2
 )
+
+type cpuMask uint32
+
+const (
+	_CPU_SETSIZE = 0x400
+	_NCPUBITS    = 0x20
+)

unix/ztypes_linux_mips64.go

@@ -791,3 +791,10 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = 0x1
 	CTRL_ATTR_MCAST_GRP_ID     = 0x2
 )
+
+type cpuMask uint64
+
+const (
+	_CPU_SETSIZE = 0x400
+	_NCPUBITS    = 0x40
+)

unix/ztypes_linux_mips64le.go

@@ -791,3 +791,10 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = 0x1
 	CTRL_ATTR_MCAST_GRP_ID     = 0x2
 )
+
+type cpuMask uint64
+
+const (
+	_CPU_SETSIZE = 0x400
+	_NCPUBITS    = 0x40
+)

unix/ztypes_linux_mipsle.go

@@ -786,3 +786,10 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = 0x1
 	CTRL_ATTR_MCAST_GRP_ID     = 0x2
 )
+
+type cpuMask uint32
+
+const (
+	_CPU_SETSIZE = 0x400
+	_NCPUBITS    = 0x20
+)

unix/ztypes_linux_ppc64.go

@@ -799,3 +799,10 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = 0x1
 	CTRL_ATTR_MCAST_GRP_ID     = 0x2
 )
+
+type cpuMask uint64
+
+const (
+	_CPU_SETSIZE = 0x400
+	_NCPUBITS    = 0x40
+)

unix/ztypes_linux_ppc64le.go

@@ -799,3 +799,10 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = 0x1
 	CTRL_ATTR_MCAST_GRP_ID     = 0x2
 )
+
+type cpuMask uint64
+
+const (
+	_CPU_SETSIZE = 0x400
+	_NCPUBITS    = 0x40
+)

unix/ztypes_linux_s390x.go

@@ -816,3 +816,10 @@ const (
 	CTRL_ATTR_MCAST_GRP_NAME   = 0x1
 	CTRL_ATTR_MCAST_GRP_ID     = 0x2
 )
+
+type cpuMask uint64
+
+const (
+	_CPU_SETSIZE = 0x400
+	_NCPUBITS    = 0x40
+)