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//go:cgo_import_dynamic libc_getrctl getrctl "libc.so"
12//go:cgo_import_dynamic libc_rctlblk_get_local_action rctlblk_get_local_action "libc.so"
13//go:cgo_import_dynamic libc_rctlblk_get_local_flags rctlblk_get_local_flags "libc.so"
14//go:cgo_import_dynamic libc_rctlblk_get_value rctlblk_get_value "libc.so"
15//go:cgo_import_dynamic libc_rctlblk_size rctlblk_size "libc.so"
16
17//go:linkname libc_getrctl libc_getrctl
18//go:linkname libc_rctlblk_get_local_action libc_rctlblk_get_local_action
19//go:linkname libc_rctlblk_get_local_flags libc_rctlblk_get_local_flags
20//go:linkname libc_rctlblk_get_value libc_rctlblk_get_value
21//go:linkname libc_rctlblk_size libc_rctlblk_size
22
23var (
24	libc_getrctl,
25	libc_rctlblk_get_local_action,
26	libc_rctlblk_get_local_flags,
27	libc_rctlblk_get_value,
28	libc_rctlblk_size libcFunc
29)
30
31// Return the minimum value seen for the zone CPU cap, or 0 if no cap is
32// detected.
33func getcpucap() uint64 {
34	// The resource control block is an opaque object whose size is only
35	// known to libc.  In practice, given the contents, it is unlikely to
36	// grow beyond 8KB so we'll use a static buffer of that size here.
37	const rblkmaxsize = 8 * 1024
38	if rctlblk_size() > rblkmaxsize {
39		return 0
40	}
41
42	// The "zone.cpu-cap" resource control, as described in
43	// resource_controls(5), "sets a limit on the amount of CPU time that
44	// can be used by a zone.  The unit used is the percentage of a single
45	// CPU that can be used by all user threads in a zone, expressed as an
46	// integer."  A C string of the name must be passed to getrctl(2).
47	name := []byte("zone.cpu-cap\x00")
48
49	// To iterate over the list of values for a particular resource
50	// control, we need two blocks: one for the previously read value and
51	// one for the next value.
52	var rblk0 [rblkmaxsize]byte
53	var rblk1 [rblkmaxsize]byte
54	rblk := &rblk0[0]
55	rblkprev := &rblk1[0]
56
57	var flag uint32 = _RCTL_FIRST
58	var capval uint64 = 0
59
60	for {
61		if getrctl(unsafe.Pointer(&name[0]), unsafe.Pointer(rblkprev), unsafe.Pointer(rblk), flag) != 0 {
62			// The end of the sequence is reported as an ENOENT
63			// failure, but determining the CPU cap is not critical
64			// here.  We'll treat any failure as if it were the end
65			// of sequence.
66			break
67		}
68
69		lflags := rctlblk_get_local_flags(unsafe.Pointer(rblk))
70		action := rctlblk_get_local_action(unsafe.Pointer(rblk))
71		if (lflags&_RCTL_LOCAL_MAXIMAL) == 0 && action == _RCTL_LOCAL_DENY {
72			// This is a finite (not maximal) value representing a
73			// cap (deny) action.
74			v := rctlblk_get_value(unsafe.Pointer(rblk))
75			if capval == 0 || capval > v {
76				capval = v
77			}
78		}
79
80		// Swap the blocks around so that we can fetch the next value
81		t := rblk
82		rblk = rblkprev
83		rblkprev = t
84		flag = _RCTL_NEXT
85	}
86
87	return capval
88}
89
90func getncpu() int32 {
91	n := int32(sysconf(__SC_NPROCESSORS_ONLN))
92	if n < 1 {
93		return 1
94	}
95
96	if cents := int32(getcpucap()); cents > 0 {
97		// Convert from a percentage of CPUs to a number of CPUs,
98		// rounding up to make use of a fractional CPU
99		// e.g., 336% becomes 4 CPUs
100		ncap := (cents + 99) / 100
101		if ncap < n {
102			return ncap
103		}
104	}
105
106	return n
107}
108
109//go:nosplit
110func getrctl(controlname, oldbuf, newbuf unsafe.Pointer, flags uint32) uintptr {
111	return sysvicall4(&libc_getrctl, uintptr(controlname), uintptr(oldbuf), uintptr(newbuf), uintptr(flags))
112}
113
114//go:nosplit
115func rctlblk_get_local_action(buf unsafe.Pointer) uintptr {
116	return sysvicall2(&libc_rctlblk_get_local_action, uintptr(buf), uintptr(0))
117}
118
119//go:nosplit
120func rctlblk_get_local_flags(buf unsafe.Pointer) uintptr {
121	return sysvicall1(&libc_rctlblk_get_local_flags, uintptr(buf))
122}
123
124//go:nosplit
125func rctlblk_get_value(buf unsafe.Pointer) uint64 {
126	return uint64(sysvicall1(&libc_rctlblk_get_value, uintptr(buf)))
127}
128
129//go:nosplit
130func rctlblk_size() uintptr {
131	return sysvicall0(&libc_rctlblk_size)
132}
133