User fewer hasher routines when there are many folders.

internal/model/model.go

@@ -17,6 +17,7 @@ import (
 	"net"
 	"os"
 	"path/filepath"
+	"runtime"
 	"strings"
 	stdsync "sync"
 	"time"
@@ -1211,7 +1212,7 @@ nextSub:
 		CurrentFiler:  cFiler{m, folder},
 		IgnorePerms:   folderCfg.IgnorePerms,
 		AutoNormalize: folderCfg.AutoNormalize,
-		Hashers:       folderCfg.Hashers,
+		Hashers:       m.numHashers(folder),
 		ShortID:       m.shortID,
 	}
 
@@ -1321,6 +1322,27 @@ nextSub:
 	return nil
 }
 
+// numHashers returns the number of hasher routines to use for a given folder,
+// taking into account configuration and available CPU cores.
+func (m *Model) numHashers(folder string) int {
+	m.fmut.Lock()
+	folderCfg := m.folderCfgs[folder]
+	numFolders := len(m.folderCfgs)
+	m.fmut.Unlock()
+
+	if folderCfg.Hashers > 0 {
+		// Specific value set in the config, use that.
+		return folderCfg.Hashers
+	}
+
+	if perFolder := runtime.GOMAXPROCS(-1) / numFolders; perFolder > 0 {
+		// We have CPUs to spare, divide them per folder.
+		return perFolder
+	}
+
+	return 1
+}
+
 // clusterConfig returns a ClusterConfigMessage that is correct for the given peer device
 func (m *Model) clusterConfig(device protocol.DeviceID) protocol.ClusterConfigMessage {
 	cm := protocol.ClusterConfigMessage{

internal/scanner/walk.go

@@ -89,14 +89,9 @@ func (w *Walker) Walk() (chan protocol.FileInfo, error) {
 		return nil, err
 	}
 
-	workers := w.Hashers
-	if workers < 1 {
-		workers = runtime.NumCPU()
-	}
-
 	files := make(chan protocol.FileInfo)
 	hashedFiles := make(chan protocol.FileInfo)
-	newParallelHasher(w.Dir, w.BlockSize, workers, hashedFiles, files)
+	newParallelHasher(w.Dir, w.BlockSize, w.Hashers, hashedFiles, files)
 
 	go func() {
 		hashFiles := w.walkAndHashFiles(files)

internal/scanner/walk_test.go

@@ -63,6 +63,7 @@ func TestWalkSub(t *testing.T) {
 		Subs:      []string{"dir2"},
 		BlockSize: 128 * 1024,
 		Matcher:   ignores,
+		Hashers:   2,
 	}
 	fchan, err := w.Walk()
 	var files []protocol.FileInfo
@@ -99,6 +100,7 @@ func TestWalk(t *testing.T) {
 		Dir:       "testdata",
 		BlockSize: 128 * 1024,
 		Matcher:   ignores,
+		Hashers:   2,
 	}
 
 	fchan, err := w.Walk()
@@ -122,6 +124,7 @@ func TestWalkError(t *testing.T) {
 	w := Walker{
 		Dir:       "testdata-missing",
 		BlockSize: 128 * 1024,
+		Hashers:   2,
 	}
 	_, err := w.Walk()
 
@@ -280,6 +283,7 @@ func walkDir(dir string) ([]protocol.FileInfo, error) {
 		Dir:           dir,
 		BlockSize:     128 * 1024,
 		AutoNormalize: true,
+		Hashers:       2,
 	}
 
 	fchan, err := w.Walk()