runtime: reintroduce ``dead'' space during GC scan
Reintroduce an optimization discarded during the initial conversion
from 4-bit heap bitmaps to 2-bit heap bitmaps: when we reach the
place in the bitmap where there are no more pointers, mark that position
for the GC so that it can avoid scanning past that place.
During heapBitsSetType we can also avoid initializing heap bitmap
beyond that location, which gives a bit of a win compared to Go 1.4.
This particular optimization (not initializing the heap bitmap) may not last:
we might change typedmemmove to use the heap bitmap, in which
case it would all need to be initialized. The early stop in the GC scan
will stay no matter what.
Compared to Go 1.4 (github.com/rsc/go, branch go14bench):
name old mean new mean delta
SetTypeNode64 80.7ns × (1.00,1.01) 57.4ns × (1.00,1.01) -28.83% (p=0.000)
SetTypeNode64Dead 80.5ns × (1.00,1.01) 13.1ns × (0.99,1.02) -83.77% (p=0.000)
SetTypeNode64Slice 2.16µs × (1.00,1.01) 1.54µs × (1.00,1.01) -28.75% (p=0.000)
SetTypeNode64DeadSlice 2.16µs × (1.00,1.01) 1.52µs × (1.00,1.00) -29.74% (p=0.000)
Compared to previous CL:
name old mean new mean delta
SetTypeNode64 56.7ns × (1.00,1.00) 57.4ns × (1.00,1.01) +1.19% (p=0.000)
SetTypeNode64Dead 57.2ns × (1.00,1.00) 13.1ns × (0.99,1.02) -77.15% (p=0.000)
SetTypeNode64Slice 1.56µs × (1.00,1.01) 1.54µs × (1.00,1.01) -0.89% (p=0.000)
SetTypeNode64DeadSlice 1.55µs × (1.00,1.01) 1.52µs × (1.00,1.00) -2.23% (p=0.000)
This is the last CL in the sequence converting from the 4-bit heap
to the 2-bit heap, with all the same optimizations reenabled.
Compared to before that process began (compared to CL 9701 patch set 1):
name old mean new mean delta
BinaryTree17 5.87s × (0.94,1.09) 5.91s × (0.96,1.06) ~ (p=0.578)
Fannkuch11 4.32s × (1.00,1.00) 4.32s × (1.00,1.00) ~ (p=0.474)
FmtFprintfEmpty 89.1ns × (0.95,1.16) 89.0ns × (0.93,1.10) ~ (p=0.942)
FmtFprintfString 283ns × (0.98,1.02) 298ns × (0.98,1.06) +5.33% (p=0.000)
FmtFprintfInt 284ns × (0.98,1.04) 286ns × (0.98,1.03) ~ (p=0.208)
FmtFprintfIntInt 486ns × (0.98,1.03) 498ns × (0.97,1.06) +2.48% (p=0.000)
FmtFprintfPrefixedInt 400ns × (0.99,1.02) 408ns × (0.98,1.02) +2.23% (p=0.000)
FmtFprintfFloat 566ns × (0.99,1.01) 587ns × (0.98,1.01) +3.69% (p=0.000)
FmtManyArgs 1.91µs × (0.99,1.02) 1.94µs × (0.99,1.02) +1.81% (p=0.000)
GobDecode 15.5ms × (0.98,1.05) 15.8ms × (0.98,1.03) +1.94% (p=0.002)
GobEncode 11.9ms × (0.97,1.03) 12.0ms × (0.96,1.09) ~ (p=0.263)
Gzip 648ms × (0.99,1.01) 648ms × (0.99,1.01) ~ (p=0.992)
Gunzip 143ms × (1.00,1.00) 143ms × (1.00,1.01) ~ (p=0.585)
HTTPClientServer 89.2µs × (0.99,1.02) 90.3µs × (0.98,1.01) +1.24% (p=0.000)
JSONEncode 32.3ms × (0.97,1.06) 31.6ms × (0.99,1.01) -2.29% (p=0.000)
JSONDecode 106ms × (0.99,1.01) 107ms × (1.00,1.01) +0.62% (p=0.000)
Mandelbrot200 6.02ms × (1.00,1.00) 6.03ms × (1.00,1.01) ~ (p=0.250)
GoParse 6.57ms × (0.97,1.06) 6.53ms × (0.99,1.03) ~ (p=0.243)
RegexpMatchEasy0_32 162ns × (1.00,1.00) 161ns × (1.00,1.01) -0.80% (p=0.000)
RegexpMatchEasy0_1K 561ns × (0.99,1.02) 541ns × (0.99,1.01) -3.67% (p=0.000)
RegexpMatchEasy1_32 145ns × (0.95,1.04) 138ns × (1.00,1.00) -5.04% (p=0.000)
RegexpMatchEasy1_1K 864ns × (0.99,1.04) 887ns × (0.99,1.01) +2.57% (p=0.000)
RegexpMatchMedium_32 255ns × (0.99,1.04) 253ns × (0.99,1.01) -1.05% (p=0.012)
RegexpMatchMedium_1K 73.9µs × (0.98,1.04) 72.8µs × (1.00,1.00) -1.51% (p=0.005)
RegexpMatchHard_32 3.92µs × (0.98,1.04) 3.85µs × (1.00,1.01) -1.88% (p=0.002)
RegexpMatchHard_1K 120µs × (0.98,1.04) 117µs × (1.00,1.01) -2.02% (p=0.001)
Revcomp 936ms × (0.95,1.08) 922ms × (0.97,1.08) ~ (p=0.234)
Template 130ms × (0.98,1.04) 126ms × (0.99,1.01) -2.99% (p=0.000)
TimeParse 638ns × (0.98,1.05) 628ns × (0.99,1.01) -1.54% (p=0.004)
TimeFormat 674ns × (0.99,1.01) 668ns × (0.99,1.01) -0.80% (p=0.001)
The slowdown of the first few benchmarks seems to be due to the new
atomic operations for certain small size allocations. But the larger
benchmarks mostly improve, probably due to the decreased memory
pressure from having half as much heap bitmap.
CL 9706, which removes the (never used anymore) wbshadow mode,
gets back what is lost in the early microbenchmarks.
Change-Id: I37423a209e8ec2a2e92538b45cac5422a6acd32d
Reviewed-on: https://go-review.googlesource.com/9705
Reviewed-by: Rick Hudson <rlh@golang.org>
diff --git a/src/cmd/internal/gc/reflect.go b/src/cmd/internal/gc/reflect.go
index 6ff9df2..061b17b 100644
--- a/src/cmd/internal/gc/reflect.go
+++ b/src/cmd/internal/gc/reflect.go
@@ -687,7 +687,7 @@
// typeptrdata returns the length in bytes of the prefix of t
// containing pointer data. Anything after this offset is scalar data.
-func typeptrdata(t *Type) uint64 {
+func typeptrdata(t *Type) int64 {
if !haspointers(t) {
return 0
}
@@ -699,24 +699,24 @@
TFUNC,
TCHAN,
TMAP:
- return uint64(Widthptr)
+ return int64(Widthptr)
case TSTRING:
// struct { byte *str; intgo len; }
- return uint64(Widthptr)
+ return int64(Widthptr)
case TINTER:
// struct { Itab *tab; void *data; } or
// struct { Type *type; void *data; }
- return 2 * uint64(Widthptr)
+ return 2 * int64(Widthptr)
case TARRAY:
if Isslice(t) {
// struct { byte *array; uintgo len; uintgo cap; }
- return uint64(Widthptr)
+ return int64(Widthptr)
}
// haspointers already eliminated t.Bound == 0.
- return uint64(t.Bound-1)*uint64(t.Type.Width) + typeptrdata(t.Type)
+ return (t.Bound-1)*t.Type.Width + typeptrdata(t.Type)
case TSTRUCT:
// Find the last field that has pointers.
@@ -726,7 +726,7 @@
lastPtrField = t1
}
}
- return uint64(lastPtrField.Width) + typeptrdata(lastPtrField.Type)
+ return lastPtrField.Width + typeptrdata(lastPtrField.Type)
default:
Fatal("typeptrdata: unexpected type, %v", t)
@@ -794,7 +794,7 @@
// zero unsafe.Pointer
// }
ot = duintptr(s, ot, uint64(t.Width))
- ot = duintptr(s, ot, typeptrdata(t))
+ ot = duintptr(s, ot, uint64(typeptrdata(t)))
ot = duint32(s, ot, typehash(t))
ot = duint8(s, ot, 0) // unused
@@ -1428,17 +1428,12 @@
}
// Calculate size of the unrolled GC mask.
- nptr := (t.Width + int64(Widthptr) - 1) / int64(Widthptr)
-
- size := (nptr + 7) / 8
+ nptr := typeptrdata(t) / int64(Widthptr)
// Decide whether to use unrolled GC mask or GC program.
// We could use a more elaborate condition, but this seems to work well in practice.
- // For small objects GC program can't give significant reduction.
- // While large objects usually contain arrays; and even if it don't
- // the program uses 2-bits per word while mask uses 4-bits per word,
- // so the program is still smaller.
- return size > int64(2*Widthptr)
+ // For small objects, the GC program can't give significant reduction.
+ return nptr > int64(2*Widthptr*8)
}
// Generates GC bitmask (1 bit per word).
@@ -1450,11 +1445,11 @@
return
}
- vec := bvalloc(2 * int32(Widthptr) * 8)
+ vec := bvalloc(int32(2 * Widthptr * 8))
xoffset := int64(0)
onebitwalktype1(t, &xoffset, vec)
- nptr := (t.Width + int64(Widthptr) - 1) / int64(Widthptr)
+ nptr := typeptrdata(t) / int64(Widthptr)
for i := int64(0); i < nptr; i++ {
if bvget(vec, int32(i)) == 1 {
gcmask[i/8] |= 1 << (uint(i) % 8)
