n_tty: Avoid false-sharing echo buffer indices
Separate the head & commit indices from the tail index to avoid
cache-line contention (so called 'false-sharing') between concurrent
threads.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 7f15b26..d4d7135 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -90,6 +90,8 @@
/* producer-published */
size_t read_head;
size_t canon_head;
+ size_t echo_head;
+ size_t echo_commit;
DECLARE_BITMAP(process_char_map, 256);
/* private to n_tty_receive_overrun (single-threaded) */
@@ -105,20 +107,17 @@
/* shared by producer and consumer */
char *read_buf;
DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE);
+ unsigned char *echo_buf;
int minimum_to_wake;
/* consumer-published */
size_t read_tail;
- unsigned char *echo_buf;
- size_t echo_head;
- size_t echo_tail;
- size_t echo_commit;
-
/* protected by output lock */
unsigned int column;
unsigned int canon_column;
+ size_t echo_tail;
struct mutex atomic_read_lock;
struct mutex output_lock;