1// Copyright 2019 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package runtime
6
7import (
8	"unsafe"
9)
10
11// Return the minimum value seen for the zone CPU cap, or 0 if no cap is
12// detected.
13func getcpucap() uint64 {
14	// The resource control block is an opaque object whose size is only
15	// known to libc.  In practice, given the contents, it is unlikely to
16	// grow beyond 8KB so we'll use a static buffer of that size here.
17	const rblkmaxsize = 8 * 1024
18	if rctlblk_size() > rblkmaxsize {
19		return 0
20	}
21
22	// The "zone.cpu-cap" resource control, as described in
23	// resource_controls(5), "sets a limit on the amount of CPU time that
24	// can be used by a zone.  The unit used is the percentage of a single
25	// CPU that can be used by all user threads in a zone, expressed as an
26	// integer."  A C string of the name must be passed to getrctl(2).
27	name := []byte("zone.cpu-cap\x00")
28
29	// To iterate over the list of values for a particular resource
30	// control, we need two blocks: one for the previously read value and
31	// one for the next value.
32	var rblk0 [rblkmaxsize]byte
33	var rblk1 [rblkmaxsize]byte
34	rblk := &rblk0[0]
35	rblkprev := &rblk1[0]
36
37	var flag uint32 = _RCTL_FIRST
38	var capval uint64 = 0
39
40	for {
41		if getrctl(unsafe.Pointer(&name[0]), unsafe.Pointer(rblkprev), unsafe.Pointer(rblk), flag) != 0 {
42			// The end of the sequence is reported as an ENOENT
43			// failure, but determining the CPU cap is not critical
44			// here.  We'll treat any failure as if it were the end
45			// of sequence.
46			break
47		}
48
49		lflags := rctlblk_get_local_flags(unsafe.Pointer(rblk))
50		action := rctlblk_get_local_action(unsafe.Pointer(rblk), 0)
51		if (lflags&_RCTL_LOCAL_MAXIMAL) == 0 && action == _RCTL_LOCAL_DENY {
52			// This is a finite (not maximal) value representing a
53			// cap (deny) action.
54			v := rctlblk_get_value(unsafe.Pointer(rblk))
55			if capval == 0 || capval > v {
56				capval = v
57			}
58		}
59
60		// Swap the blocks around so that we can fetch the next value
61		t := rblk
62		rblk = rblkprev
63		rblkprev = t
64		flag = _RCTL_NEXT
65	}
66
67	return capval
68}
69
70func getncpu() int32 {
71	n := int32(sysconf(__SC_NPROCESSORS_ONLN))
72	if n < 1 {
73		return 1
74	}
75
76	if cents := int32(getcpucap()); cents > 0 {
77		// Convert from a percentage of CPUs to a number of CPUs,
78		// rounding up to make use of a fractional CPU
79		// e.g., 336% becomes 4 CPUs
80		ncap := (cents + 99) / 100
81		if ncap < n {
82			return ncap
83		}
84	}
85
86	return n
87}
88
89//extern getrctl
90func getrctl(controlname, oldbuf, newbuf unsafe.Pointer, flags uint32) int32
91
92//extern rctlblk_get_local_action
93func rctlblk_get_local_action(buf, signalp unsafe.Pointer) uint32
94
95//extern rctlblk_get_local_flags
96func rctlblk_get_local_flags(buf unsafe.Pointer) uint32
97
98//extern rctlblk_get_value
99func rctlblk_get_value(buf unsafe.Pointer) uint64
100
101//extern rctlblk_size
102func rclblk_size() uintptr
103