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runtime: iterate over set bits in adjustpointers

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There are several things combined in this change.

First, eliminate the gobitvector type in favor
of adding a ptrbit method to bitvector.
In non-performance-critical code, use that method.
In performance critical code, though, load the bitvector data
one byte at a time and iterate only over set bits.
To support that, add and use sys.Ctz8.

name                old time/op  new time/op  delta
StackCopyPtr-8      81.8ms ± 5%  78.9ms ± 3%   -3.58%  (p=0.000 n=97+96)
StackCopy-8         65.9ms ± 3%  62.8ms ± 3%   -4.67%  (p=0.000 n=96+92)
StackCopyNoCache-8   105ms ± 3%   102ms ± 3%   -3.38%  (p=0.000 n=96+95)

Change-Id: I00b80f45612708bd440b1a411a57fa6dfa24aa74
Reviewed-on: https://go-review.googlesource.com/109716
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Josh Bleecher Snyder 2018-04-01 11:01:36 -07:00
parent 13cd006139
commit 5af0b28a73
7 changed files with 76 additions and 47 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/cmd/compile/internal/gc/ssa.go
View File

@ -2980,6 +2980,8 @@ func init() {
alias("runtime/internal/atomic", "Casp1", "runtime/internal/atomic", "Cas", p4...)
alias("runtime/internal/atomic", "Casp1", "runtime/internal/atomic", "Cas64", p8...)
alias("runtime/internal/sys", "Ctz8", "math/bits", "TrailingZeros8", all...)
/******** math ********/
addF("math", "Sqrt",
func(s *state, n *Node, args []*ssa.Value) *ssa.Value {

5
src/runtime/heapdump.go
View File

@ -233,9 +233,8 @@ type childInfo struct {
// dump kinds & offsets of interesting fields in bv
func dumpbv(cbv *bitvector, offset uintptr) {
bv := gobv(*cbv)
for i := uintptr(0); i < bv.n; i++ {
if bv.bytedata[i/8]>>(i%8)&1 == 1 {
for i := uintptr(0); i < uintptr(cbv.n); i++ {
if cbv.ptrbit(i) == 1 {
dumpint(fieldKindPtr)
dumpint(uint64(offset + i*sys.PtrSize))
}

24
src/runtime/internal/sys/intrinsics.go
View File

@ -50,6 +50,30 @@ func Ctz32(x uint32) int {
return i + z
}
// Ctz8 returns the number of trailing zero bits in x; the result is 8 for x == 0.
func Ctz8(x uint8) int {
return int(ntz8tab[x])
}
var ntz8tab = [256]uint8{
0x08, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x05, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x06, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x05, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x07, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x05, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x06, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x05, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x00, 0x02, 0x00, 0x01, 0x00,
}
// Bswap64 returns its input with byte order reversed
// 0x0102030405060708 -> 0x0807060504030201
func Bswap64(x uint64) uint64 {

8
src/runtime/internal/sys/intrinsics_386.s
View File

@ -34,6 +34,14 @@ TEXT runtime∕internal∕sys·Ctz32(SB), NOSPLIT, $0-8
MOVL AX, ret+4(FP)
RET
TEXT runtime∕internal∕sys·Ctz8(SB), NOSPLIT, $0-8
MOVBLZX x+0(FP), AX
BSFL AX, AX
JNZ 2(PC)
MOVL $8, AX
MOVL AX, ret+4(FP)
RET
TEXT runtime∕internal∕sys·Bswap64(SB), NOSPLIT, $0-16
MOVL x_lo+0(FP), AX
MOVL x_hi+4(FP), BX

1
src/runtime/internal/sys/intrinsics_stubs.go
View File

@ -8,5 +8,6 @@ package sys
func Ctz64(x uint64) int
func Ctz32(x uint32) int
func Ctz8(x uint8) int
func Bswap64(x uint64) uint64
func Bswap32(x uint32) uint32

3
src/runtime/mbitmap.go
View File

@ -2021,9 +2021,8 @@ func getgcmask(ep interface{}) (mask []byte) {
n := (*ptrtype)(unsafe.Pointer(t)).elem.size
mask = make([]byte, n/sys.PtrSize)
for i := uintptr(0); i < n; i += sys.PtrSize {
bitmap := bv.bytedata
off := (uintptr(p) + i - frame.varp + size) / sys.PtrSize
mask[i/sys.PtrSize] = (*addb(bitmap, off/8) >> (off % 8)) & 1
mask[i/sys.PtrSize] = bv.ptrbit(off)
}
}
return

80
src/runtime/stack.go
View File

@ -544,64 +544,60 @@ type bitvector struct {
bytedata *uint8
}
type gobitvector struct {
n uintptr
bytedata []uint8
}
func gobv(bv bitvector) gobitvector {
return gobitvector{
uintptr(bv.n),
(*[1 << 30]byte)(unsafe.Pointer(bv.bytedata))[:(bv.n+7)/8],
}
}
func ptrbit(bv *gobitvector, i uintptr) uint8 {
return (bv.bytedata[i/8] >> (i % 8)) & 1
// ptrbit returns the i'th bit in bv.
// ptrbit is less efficient than iterating directly over bitvector bits,
// and should only be used in non-performance-critical code.
// See adjustpointers for an example of a high-efficiency walk of a bitvector.
func (bv *bitvector) ptrbit(i uintptr) uint8 {
b := *(addb(bv.bytedata, i/8))
return (b >> (i % 8)) & 1
}
// bv describes the memory starting at address scanp.
// Adjust any pointers contained therein.
func adjustpointers(scanp unsafe.Pointer, cbv *bitvector, adjinfo *adjustinfo, f funcInfo) {
bv := gobv(*cbv)
func adjustpointers(scanp unsafe.Pointer, bv *bitvector, adjinfo *adjustinfo, f funcInfo) {
minp := adjinfo.old.lo
maxp := adjinfo.old.hi
delta := adjinfo.delta
num := bv.n
num := uintptr(bv.n)
// If this frame might contain channel receive slots, use CAS
// to adjust pointers. If the slot hasn't been received into
// yet, it may contain stack pointers and a concurrent send
// could race with adjusting those pointers. (The sent value
// itself can never contain stack pointers.)
useCAS := uintptr(scanp) < adjinfo.sghi
for i := uintptr(0); i < num; i++ {
for i := uintptr(0); i < num; i += 8 {
if stackDebug >= 4 {
print(" ", add(scanp, i*sys.PtrSize), ":", ptrnames[ptrbit(&bv, i)], ":", hex(*(*uintptr)(add(scanp, i*sys.PtrSize))), " # ", i, " ", bv.bytedata[i/8], "\n")
}
if ptrbit(&bv, i) != 1 {
continue
}
pp := (*uintptr)(add(scanp, i*sys.PtrSize))
retry:
p := *pp
if f.valid() && 0 < p && p < minLegalPointer && debug.invalidptr != 0 {
// Looks like a junk value in a pointer slot.
// Live analysis wrong?
getg().m.traceback = 2
print("runtime: bad pointer in frame ", funcname(f), " at ", pp, ": ", hex(p), "\n")
throw("invalid pointer found on stack")
}
if minp <= p && p < maxp {
if stackDebug >= 3 {
print("adjust ptr ", hex(p), " ", funcname(f), "\n")
for j := uintptr(0); j < 8; j++ {
print(" ", add(scanp, (i+j)*sys.PtrSize), ":", ptrnames[bv.ptrbit(i+j)], ":", hex(*(*uintptr)(add(scanp, (i+j)*sys.PtrSize))), " # ", i, " ", *addb(bv.bytedata, i/8), "\n")
}
if useCAS {
ppu := (*unsafe.Pointer)(unsafe.Pointer(pp))
if !atomic.Casp1(ppu, unsafe.Pointer(p), unsafe.Pointer(p+delta)) {
goto retry
}
b := *(addb(bv.bytedata, i/8))
for b != 0 {
j := uintptr(sys.Ctz8(b))
b &= b - 1
pp := (*uintptr)(add(scanp, (i+j)*sys.PtrSize))
retry:
p := *pp
if f.valid() && 0 < p && p < minLegalPointer && debug.invalidptr != 0 {
// Looks like a junk value in a pointer slot.
// Live analysis wrong?
getg().m.traceback = 2
print("runtime: bad pointer in frame ", funcname(f), " at ", pp, ": ", hex(p), "\n")
throw("invalid pointer found on stack")
}
if minp <= p && p < maxp {
if stackDebug >= 3 {
print("adjust ptr ", hex(p), " ", funcname(f), "\n")
}
if useCAS {
ppu := (*unsafe.Pointer)(unsafe.Pointer(pp))
if !atomic.Casp1(ppu, unsafe.Pointer(p), unsafe.Pointer(p+delta)) {
goto retry
}
} else {
*pp = p + delta
}
} else {
*pp = p + delta
}
}
}