internal/impl: avoid inlining fixed coderFieldInfo array
Any attempt at guessing the size for a fixed coderFieldInfo array
will always get it wrong in some cases, either by under-estimating
or over-estimating the count. The former causes worse caching behavior,
while the latter causes memory waste.
As a middle ground, just pre-allocate a slice of the exact length.
Each element will have memory locality with each other, but not
be guaranteed to have memory locality with the parent coderMessageInfo.
name old time/op new time/op delta
EmptyMessage/Wire/Marshal-8 43.1ns ±11% 42.6ns ± 8% -1.32% (p=0.036 n=50+49)
EmptyMessage/Wire/Unmarshal-8 18.6ns ±10% 18.9ns ±12% ~ (p=0.054 n=50+50)
EmptyMessage/Wire/Validate-8 15.0ns ± 9% 14.7ns ±10% -2.44% (p=0.002 n=50+45)
EmptyMessage/Clone-8 163ns ±20% 149ns ±19% -8.58% (p=0.000 n=48+53)
RepeatedInt32/Wire/Marshal-8 4.27µs ±12% 4.24µs ±13% ~ (p=0.612 n=48+52)
RepeatedInt32/Wire/Unmarshal-8 3.47µs ±14% 3.50µs ±11% ~ (p=0.217 n=50+53)
RepeatedInt32/Wire/Validate-8 2.12µs ±12% 2.09µs ± 9% ~ (p=0.121 n=50+51)
RepeatedInt32/Clone-8 3.04µs ±18% 2.98µs ±36% ~ (p=0.289 n=51+54)
Required/Wire/Marshal-8 281ns ±14% 276ns ±11% ~ (p=0.059 n=48+55)
Required/Wire/Unmarshal-8 117ns ±14% 118ns ±11% ~ (p=0.358 n=49+53)
Required/Wire/Validate-8 87.6ns ± 9% 88.0ns ±12% ~ (p=0.373 n=48+53)
Required/Clone-8 533ns ±12% 507ns ±15% -4.71% (p=0.000 n=49+54)
Change-Id: I4cf3134e424130bee728b7591127e5c80f07e2db
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/232937
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/impl/codec_message.go b/internal/impl/codec_message.go
index 29ed59b..0e176d5 100644
--- a/internal/impl/codec_message.go
+++ b/internal/impl/codec_message.go
@@ -31,11 +31,6 @@
needsInitCheck bool
isMessageSet bool
numRequiredFields uint8
-
- // Include space for a number of coderFieldInfos to improve cache locality.
- // The number of entries is chosen through a combination of guesswork and
- // empirical testing.
- coderFieldBuf [32]coderFieldInfo
}
type coderFieldInfo struct {
@@ -58,7 +53,7 @@
mi.coderFields = make(map[protowire.Number]*coderFieldInfo)
fields := mi.Desc.Fields()
- preallocFields := mi.coderFieldBuf[:]
+ preallocFields := make([]coderFieldInfo, fields.Len())
for i := 0; i < fields.Len(); i++ {
fd := fields.Get(i)
@@ -87,13 +82,7 @@
fieldOffset = offsetOf(fs, mi.Exporter)
childMessage, funcs = fieldCoder(fd, ft)
}
- var cf *coderFieldInfo
- if len(preallocFields) > 0 {
- cf = &preallocFields[0]
- preallocFields = preallocFields[1:]
- } else {
- cf = new(coderFieldInfo)
- }
+ cf := &preallocFields[i]
*cf = coderFieldInfo{
num: fd.Number(),
offset: fieldOffset,
