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69261ecad6
The hardware divider is an optional component of ARMv7. This patch detects whether it is available in runtime and use it or not. 1. The hardware divider is detected at startup and a flag is set/clear according to a perticular bit of runtime.hwcap. 2. Each call of runtime.udiv will check this flag and decide if use the hardware division instruction. A rough test shows the performance improves 40-50% for ARMv7. And the compatibility of ARMv5/v6 is not broken. fixes #19118 Change-Id: Ic586bc9659ebc169553ca2004d2bdb721df823ac Reviewed-on: https://go-review.googlesource.com/37496 Run-TryBot: Cherry Zhang <cherryyz@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Cherry Zhang <cherryyz@google.com>
69 lines
2.1 KiB
Go
69 lines
2.1 KiB
Go
// Copyright 2009 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 "unsafe"
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const (
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_AT_PLATFORM = 15 // introduced in at least 2.6.11
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_HWCAP_VFP = 1 << 6 // introduced in at least 2.6.11
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_HWCAP_VFPv3 = 1 << 13 // introduced in 2.6.30
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_HWCAP_IDIVA = 1 << 17
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)
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var randomNumber uint32
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var armArch uint8 = 6 // we default to ARMv6
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var hwcap uint32 // set by setup_auxv
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var hardDiv bool // set if a hardware divider is available
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func checkgoarm() {
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// On Android, /proc/self/auxv might be unreadable and hwcap won't
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// reflect the CPU capabilities. Assume that every Android arm device
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// has the necessary floating point hardware available.
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if GOOS == "android" {
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return
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}
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if goarm > 5 && hwcap&_HWCAP_VFP == 0 {
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print("runtime: this CPU has no floating point hardware, so it cannot run\n")
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print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
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exit(1)
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}
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if goarm > 6 && hwcap&_HWCAP_VFPv3 == 0 {
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print("runtime: this CPU has no VFPv3 floating point hardware, so it cannot run\n")
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print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
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exit(1)
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}
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}
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func archauxv(tag, val uintptr) {
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switch tag {
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case _AT_RANDOM:
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// sysargs filled in startupRandomData, but that
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// pointer may not be word aligned, so we must treat
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// it as a byte array.
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randomNumber = uint32(startupRandomData[4]) | uint32(startupRandomData[5])<<8 |
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uint32(startupRandomData[6])<<16 | uint32(startupRandomData[7])<<24
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case _AT_PLATFORM: // v5l, v6l, v7l
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t := *(*uint8)(unsafe.Pointer(val + 1))
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if '5' <= t && t <= '7' {
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armArch = t - '0'
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}
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case _AT_HWCAP: // CPU capability bit flags
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hwcap = uint32(val)
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hardDiv = (hwcap & _HWCAP_IDIVA) != 0
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}
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}
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//go:nosplit
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func cputicks() int64 {
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// Currently cputicks() is used in blocking profiler and to seed fastrand().
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// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
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// randomNumber provides better seeding of fastrand.
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return nanotime() + int64(randomNumber)
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}
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