cmd/link: use BestSpeed for DWARF compression
DWARF compression accounts for roughly 30% of the linker's time. This
CL switches from DefaultCompression to BestSpeed, which virtually
eliminates this time. This roughly halves the overhead of handling
DWARF in the linker:
name \ time/op nodwarf dwarf dwarf-speed
BuildCmdGoAll 10.0s ±11% 10.6s ± 5% 10.8s ± 5%
nodwarf +6.41% +8.03%
dwarf ~
LinkCmdGo 626ms ± 5% 1096ms ± 2% 860ms ± 2%
nodwarf +75.17% +37.36%
dwarf -21.59%
Previously, enabling DWARF had a 75% overhead in link time for cmd/go.
This change reduces this overhead to 37% (a 22% reduction).
The effect on binary size is minimal compared to DefaultCompression,
and still substantially better than no compression:
cmd/go bytes
nodwarf 10106953
dwarf 12159049 nodwarf+20%
dwarf-speed 12408905 nodwarf+23%
dwarf-nozlib 17766473 nodwarf+76%
Updates #26318.
Change-Id: I33bb7caa038a2753c29104501663daf4839e7054
Reviewed-on: https://go-review.googlesource.com/123356
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index c337c5e..0ae93f1 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -2177,7 +2177,14 @@
binary.BigEndian.PutUint64(sizeBytes[:], uint64(total))
buf.Write(sizeBytes[:])
- z := zlib.NewWriter(&buf)
+ // Using zlib.BestSpeed achieves very nearly the same
+ // compression levels of zlib.DefaultCompression, but takes
+ // substantially less time. This is important because DWARF
+ // compression can be a significant fraction of link time.
+ z, err := zlib.NewWriterLevel(&buf, zlib.BestSpeed)
+ if err != nil {
+ log.Fatalf("NewWriterLevel failed: %s", err)
+ }
for _, sym := range syms {
if _, err := z.Write(sym.P); err != nil {
log.Fatalf("compression failed: %s", err)
