runtime: use vDSO for clock_gettime on linux/arm64

Use the __vdso_clock_gettime fast path via the vDSO on linux/arm64 to
speed up nanotime and walltime. This results in the following
performance improvement for time.Now on Cavium ThunderX:

name     old time/op  new time/op  delta
TimeNow   442ns ± 0%   163ns ± 0%  -63.16%  (p=0.000 n=10+10)

And benchmarks on VDSO

BenchmarkClockVDSOAndFallbackPaths/vDSO         10000000 166 ns/op
BenchmarkClockVDSOAndFallbackPaths/Fallback     3000000 456 ns/op

Change-Id: I326118c6dff865eaa0569fc45d1fc1ff95cb74f6
Reviewed-on: https://go-review.googlesource.com/99855
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/os_linux_novdso.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build linux
-// +build !386,!amd64,!arm
+// +build !386,!amd64,!arm,!arm64
 
 package runtime
 

src/runtime/sys_linux_arm64.s

@@ -12,6 +12,9 @@
 
 #define AT_FDCWD -100
 
+#define CLOCK_REALTIME 0
+#define CLOCK_MONOTONIC 1
+
 #define SYS_exit		93
 #define SYS_read		63
 #define SYS_write		64
@@ -180,23 +183,87 @@ TEXT runtime·mincore(SB),NOSPLIT|NOFRAME,$0-28
 
 // func walltime() (sec int64, nsec int32)
 TEXT runtime·walltime(SB),NOSPLIT,$24-12
-	MOVW	$0, R0 // CLOCK_REALTIME
+	MOVD	RSP, R20	// R20 is unchanged by C code
 	MOVD	RSP, R1
+
+	MOVD	g_m(g), R21	// R21 = m
+
+	// Set vdsoPC and vdsoSP for SIGPROF traceback.
+	MOVD	LR, m_vdsoPC(R21)
+	MOVD	R20, m_vdsoSP(R21)
+
+	MOVD	m_curg(R21), R0
+	CMP	g, R0
+	BNE	noswitch
+
+	MOVD	m_g0(R21), R3
+	MOVD	(g_sched+gobuf_sp)(R3), R1	// Set RSP to g0 stack
+
+noswitch:
+	SUB	$16, R1
+	BIC	$15, R1	// Align for C code
+	MOVD	R1, RSP
+
+	MOVW	$CLOCK_REALTIME, R0
+	MOVD	runtime·vdsoClockgettimeSym(SB), R2
+	CBZ	R2, fallback
+	BL	(R2)
+	B	finish
+
+fallback:
 	MOVD	$SYS_clock_gettime, R8
 	SVC
+
+finish:
 	MOVD	0(RSP), R3	// sec
 	MOVD	8(RSP), R5	// nsec
+
+	MOVD	R20, RSP	// restore SP
+	MOVD	$0, m_vdsoSP(R21)	// clear vdsoSP
+
 	MOVD	R3, sec+0(FP)
 	MOVW	R5, nsec+8(FP)
 	RET
 
 TEXT runtime·nanotime(SB),NOSPLIT,$24-8
-	MOVW	$1, R0 // CLOCK_MONOTONIC
+	MOVD	RSP, R20	// R20 is unchanged by C code
 	MOVD	RSP, R1
+
+	MOVD	g_m(g), R21	// R21 = m
+
+	// Set vdsoPC and vdsoSP for SIGPROF traceback.
+	MOVD	LR, m_vdsoPC(R21)
+	MOVD	R20, m_vdsoSP(R21)
+
+	MOVD	m_curg(R21), R0
+	CMP	g, R0
+	BNE	noswitch
+
+	MOVD	m_g0(R21), R3
+	MOVD	(g_sched+gobuf_sp)(R3), R1	// Set RSP to g0 stack
+
+noswitch:
+	SUB	$16, R1
+	BIC	$15, R1
+	MOVD	R1, RSP
+
+	MOVW	$CLOCK_MONOTONIC, R0
+	MOVD	runtime·vdsoClockgettimeSym(SB), R2
+	CBZ	R2, fallback
+	BL	(R2)
+	B	finish
+
+fallback:
 	MOVD	$SYS_clock_gettime, R8
 	SVC
+
+finish:
 	MOVD	0(RSP), R3	// sec
 	MOVD	8(RSP), R5	// nsec
+
+	MOVD	R20, RSP	// restore SP
+	MOVD	$0, m_vdsoSP(R21)	// clear vdsoSP
+
 	// sec is in R3, nsec in R5
 	// return nsec in R3
 	MOVD	$1000000000, R4

src/runtime/vdso_elf64.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build linux
-// +build amd64
+// +build amd64 arm64
 
 package runtime
 

src/runtime/vdso_in_none.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux,!386,!amd64,!arm !linux
+// +build linux,!386,!amd64,!arm,!arm64 !linux
 
 package runtime
 

src/runtime/vdso_linux.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build linux
-// +build 386 amd64 arm
+// +build 386 amd64 arm arm64
 
 package runtime
 
@@ -96,8 +96,6 @@ type vdsoInfo struct {
 	verdef *elfVerdef
 }
 
-var linux26 = vdsoVersionKey{"LINUX_2.6", 0x3ae75f6}
-
 // see vdso_linux_*.go for vdsoSymbolKeys[] and vdso*Sym vars
 
 func vdsoInitFromSysinfoEhdr(info *vdsoInfo, hdr *elfEhdr) {
@@ -220,7 +218,6 @@ func vdsoParseSymbols(info *vdsoInfo, version int32) {
 		if k.name != gostringnocopy(&info.symstrings[sym.st_name]) {
 			return false
 		}
-
 		// Check symbol version.
 		if info.versym != nil && version != 0 && int32(info.versym[symIndex]&0x7fff) != version {
 			return false
@@ -276,7 +273,7 @@ func vdsoauxv(tag, val uintptr) {
 		// when passed to the three functions below.
 		info1 := (*vdsoInfo)(noescape(unsafe.Pointer(&info)))
 		vdsoInitFromSysinfoEhdr(info1, (*elfEhdr)(unsafe.Pointer(val)))
-		vdsoParseSymbols(info1, vdsoFindVersion(info1, &linux26))
+		vdsoParseSymbols(info1, vdsoFindVersion(info1, &vdsoLinuxVersion))
 	}
 }
 

src/runtime/vdso_linux_386.go

@@ -11,11 +11,11 @@ const (
 	vdsoArrayMax = 1<<31 - 1
 )
 
+var vdsoLinuxVersion = vdsoVersionKey{"LINUX_2.6", 0x3ae75f6}
+
 var vdsoSymbolKeys = []vdsoSymbolKey{
 	{"__vdso_clock_gettime", 0xd35ec75, 0x6e43a318, &vdsoClockgettimeSym},
 }
 
 // initialize to fall back to syscall
-var (
-	vdsoClockgettimeSym uintptr = 0
-)
+var vdsoClockgettimeSym uintptr = 0

src/runtime/vdso_linux_amd64.go

@@ -10,6 +10,8 @@ const (
 	vdsoArrayMax = 1<<50 - 1
 )
 
+var vdsoLinuxVersion = vdsoVersionKey{"LINUX_2.6", 0x3ae75f6}
+
 var vdsoSymbolKeys = []vdsoSymbolKey{
 	{"__vdso_gettimeofday", 0x315ca59, 0xb01bca00, &vdsoGettimeofdaySym},
 	{"__vdso_clock_gettime", 0xd35ec75, 0x6e43a318, &vdsoClockgettimeSym},

src/runtime/vdso_linux_arm.go

@@ -11,6 +11,8 @@ const (
 	vdsoArrayMax = 1<<31 - 1
 )
 
+var vdsoLinuxVersion = vdsoVersionKey{"LINUX_2.6", 0x3ae75f6}
+
 var vdsoSymbolKeys = []vdsoSymbolKey{
 	{"__vdso_clock_gettime", 0xd35ec75, 0x6e43a318, &vdsoClockgettimeSym},
 }

src/runtime/vdso_linux_arm64.go

+// Copyright 2018 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
+
+const (
+	// vdsoArrayMax is the byte-size of a maximally sized array on this architecture.
+	// See cmd/compile/internal/arm64/galign.go arch.MAXWIDTH initialization.
+	vdsoArrayMax = 1<<50 - 1
+)
+
+// key and version at man 7 vdso : aarch64
+var vdsoLinuxVersion = vdsoVersionKey{"LINUX_2.6.39", 0x75fcb89}
+
+var vdsoSymbolKeys = []vdsoSymbolKey{
+	{"__kernel_clock_gettime", 0xd35ec75, 0x6e43a318, &vdsoClockgettimeSym},
+}
+
+// initialize to fall back to syscall
+var vdsoClockgettimeSym uintptr = 0

src/runtime/vdso_linux_test.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build linux
-// +build 386 amd64 arm
+// +build 386 amd64 arm arm64
 
 package runtime_test