From 491615e3f7acca2964744307adf3655eb3e778b2 Mon Sep 17 00:00:00 2001
From: Jeremy Faller <jeremy@golang.org>
Date: Mon, 24 Feb 2020 21:08:12 -0500
Subject: [PATCH] [dev.link] cmd/link: parallelize reloc sym
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I tried a couple of different architectures (goroutine per symbol, 8
goroutines handling symbols from channels, and this architecture), and
this was the best. Another possible approach could be to divide up the
space of relocations, forgo the channels, and just pass slices to the
relocation routines, which would possibly be faster.

Reloc                     13.9ms ± 5%      9.0ms ±10%       -35.09%  (p=0.000 n=8+9)

Change-Id: I5111220e855313fae4b89d64277759c4dc33b697
Reviewed-on: https://go-review.googlesource.com/c/go/+/220842
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
---
 src/cmd/link/internal/ld/data.go | 30 +++++++++++++++++++++---------
 1 file changed, 21 insertions(+), 9 deletions(-)

diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index 629cd5cd27..25dda36293 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -571,19 +571,31 @@ func relocsym(target *Target, err *ErrorReporter, lookup LookupFn, syms *ArchSym
 }
 
 func (ctxt *Link) reloc() {
+	var wg sync.WaitGroup
 	target := &ctxt.Target
 	reporter := &ctxt.ErrorReporter
 	lookup := ctxt.Syms.ROLookup
 	syms := &ctxt.ArchSyms
-	for _, s := range ctxt.Textp {
-		relocsym(target, reporter, lookup, syms, s)
-	}
-	for _, s := range datap {
-		relocsym(target, reporter, lookup, syms, s)
-	}
-	for _, s := range dwarfp {
-		relocsym(target, reporter, lookup, syms, s)
-	}
+	wg.Add(3)
+	go func() {
+		for _, s := range ctxt.Textp {
+			relocsym(target, reporter, lookup, syms, s)
+		}
+		wg.Done()
+	}()
+	go func() {
+		for _, s := range datap {
+			relocsym(target, reporter, lookup, syms, s)
+		}
+		wg.Done()
+	}()
+	go func() {
+		for _, s := range dwarfp {
+			relocsym(target, reporter, lookup, syms, s)
+		}
+		wg.Done()
+	}()
+	wg.Wait()
 }
 
 func windynrelocsym(ctxt *Link, rel, s *sym.Symbol) {
-- 
2.48.1