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// Copyright 2019 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.
package runtime
import (
"unsafe"
)
// Return the minimum value seen for the zone CPU cap, or 0 if no cap is
// detected.
func getcpucap() uint64 {
// The resource control block is an opaque object whose size is only
// known to libc. In practice, given the contents, it is unlikely to
// grow beyond 8KB so we'll use a static buffer of that size here.
const rblkmaxsize = 8 * 1024
if rctlblk_size() > rblkmaxsize {
return 0
}
// The "zone.cpu-cap" resource control, as described in
// resource_controls(5), "sets a limit on the amount of CPU time that
// can be used by a zone. The unit used is the percentage of a single
// CPU that can be used by all user threads in a zone, expressed as an
// integer." A C string of the name must be passed to getrctl(2).
name := []byte("zone.cpu-cap\x00")
// To iterate over the list of values for a particular resource
// control, we need two blocks: one for the previously read value and
// one for the next value.
var rblk0 [rblkmaxsize]byte
var rblk1 [rblkmaxsize]byte
rblk := &rblk0[0]
rblkprev := &rblk1[0]
var flag uint32 = _RCTL_FIRST
var capval uint64 = 0
for {
if getrctl(unsafe.Pointer(&name[0]), unsafe.Pointer(rblkprev), unsafe.Pointer(rblk), flag) != 0 {
// The end of the sequence is reported as an ENOENT
// failure, but determining the CPU cap is not critical
// here. We'll treat any failure as if it were the end
// of sequence.
break
}
lflags := rctlblk_get_local_flags(unsafe.Pointer(rblk))
action := rctlblk_get_local_action(unsafe.Pointer(rblk), 0)
if (lflags&_RCTL_LOCAL_MAXIMAL) == 0 && action == _RCTL_LOCAL_DENY {
// This is a finite (not maximal) value representing a
// cap (deny) action.
v := rctlblk_get_value(unsafe.Pointer(rblk))
if capval == 0 || capval > v {
capval = v
}
}
// Swap the blocks around so that we can fetch the next value
t := rblk
rblk = rblkprev
rblkprev = t
flag = _RCTL_NEXT
}
return capval
}
func getncpu() int32 {
n := int32(sysconf(__SC_NPROCESSORS_ONLN))
if n < 1 {
return 1
}
if cents := int32(getcpucap()); cents > 0 {
// Convert from a percentage of CPUs to a number of CPUs,
// rounding up to make use of a fractional CPU
// e.g., 336% becomes 4 CPUs
ncap := (cents + 99) / 100
if ncap < n {
return ncap
}
}
return n
}
//extern getrctl
func getrctl(controlname, oldbuf, newbuf unsafe.Pointer, flags uint32) int32
//extern rctlblk_get_local_action
func rctlblk_get_local_action(buf, signalp unsafe.Pointer) uint32
//extern rctlblk_get_local_flags
func rctlblk_get_local_flags(buf unsafe.Pointer) uint32
//extern rctlblk_get_value
func rctlblk_get_value(buf unsafe.Pointer) uint64
//extern rctlblk_size
func rclblk_size() uintptr
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