vgacon: optimize scrolling

Join multiple scr_memcpyw into 1-3 calls (usually 2).  (benchmarked
average speedup: 1%)

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Cc: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/console/vgacon.c

@@ -292,23 +292,26 @@ static int vgacon_scrolldelta(struct vc_data *c, int lines)
 	d = (void *) c->vc_origin;
 	s = (void *) c->vc_screenbuf;
 
-	while (count--) {
-		scr_memcpyw(d, vgacon_scrollback + soff, c->vc_size_row);
-		d += c->vc_size_row;
-		soff += c->vc_size_row;
-
-		if (soff >= vgacon_scrollback_size)
-			soff = 0;
+	if (count) {
+		int copysize;
+		count *= c->vc_size_row;
+		/* how much memory to end of buffer left? */
+		copysize = min(count, vgacon_scrollback_size - soff);
+		scr_memcpyw(d, vgacon_scrollback + soff, copysize);
+		d += copysize;
+		count -= copysize;
+
+		if (count) {
+			scr_memcpyw(d, vgacon_scrollback, count);
+			d += count;
+		}
 	}
 
 	if (diff == c->vc_rows) {
 		vgacon_cursor(c, CM_MOVE);
 	} else {
-		while (diff--) {
-			scr_memcpyw(d, s, c->vc_size_row);
-			d += c->vc_size_row;
-			s += c->vc_size_row;
-		}
+		if (diff)
+			scr_memcpyw(d, s, diff * c->vc_size_row);
 	}
 
 	return 1;