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