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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"
)
//go:cgo_import_dynamic libc_getrctl getrctl "libc.so"
//go:cgo_import_dynamic libc_rctlblk_get_local_action rctlblk_get_local_action "libc.so"
//go:cgo_import_dynamic libc_rctlblk_get_local_flags rctlblk_get_local_flags "libc.so"
//go:cgo_import_dynamic libc_rctlblk_get_value rctlblk_get_value "libc.so"
//go:cgo_import_dynamic libc_rctlblk_size rctlblk_size "libc.so"
//go:linkname libc_getrctl libc_getrctl
//go:linkname libc_rctlblk_get_local_action libc_rctlblk_get_local_action
//go:linkname libc_rctlblk_get_local_flags libc_rctlblk_get_local_flags
//go:linkname libc_rctlblk_get_value libc_rctlblk_get_value
//go:linkname libc_rctlblk_size libc_rctlblk_size
var (
libc_getrctl,
libc_rctlblk_get_local_action,
libc_rctlblk_get_local_flags,
libc_rctlblk_get_value,
libc_rctlblk_size libcFunc
)
// 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))
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
}
//go:nosplit
func getrctl(controlname, oldbuf, newbuf unsafe.Pointer, flags uint32) uintptr {
return sysvicall4(&libc_getrctl, uintptr(controlname), uintptr(oldbuf), uintptr(newbuf), uintptr(flags))
}
//go:nosplit
func rctlblk_get_local_action(buf unsafe.Pointer) uintptr {
return sysvicall2(&libc_rctlblk_get_local_action, uintptr(buf), uintptr(0))
}
//go:nosplit
func rctlblk_get_local_flags(buf unsafe.Pointer) uintptr {
return sysvicall1(&libc_rctlblk_get_local_flags, uintptr(buf))
}
//go:nosplit
func rctlblk_get_value(buf unsafe.Pointer) uint64 {
return uint64(sysvicall1(&libc_rctlblk_get_value, uintptr(buf)))
}
//go:nosplit
func rctlblk_size() uintptr {
return sysvicall0(&libc_rctlblk_size)
}