Increase disk I/O semaphore limit (#6449)

This updates `dios` to range up to 50% of the core count on a system
with more than 32 CPU cores, otherwise obeying the 4 to 16 limit.

Signed-off-by: Neil Twigg <neil@nats.io>

server/filestore.go

@@ -10007,8 +10007,14 @@ var dios chan struct{}
 // golang.org's semaphore seemed a bit heavy.
 func init() {
 	// Limit ourselves to a sensible number of blocking I/O calls. Range between
-	// 4-16 concurrent disk I/Os based on the number of CPU cores available.
-	nIO := min(16, max(4, runtime.GOMAXPROCS(-1)))
+	// 4-16 concurrent disk I/Os based on CPU cores, or 50% of cores if greater
+	// than 32 cores.
+	mp := runtime.GOMAXPROCS(-1)
+	nIO := min(16, max(4, mp))
+	if mp > 32 {
+		// If the system has more than 32 cores then limit dios to 50% of cores.
+		nIO = max(16, min(mp, mp/2))
+	}
 	dios = make(chan struct{}, nIO)
 	// Fill it up to start.
 	for i := 0; i < nIO; i++ {