If the read buffer indices are in the same cache-line, cpus will
contended over the cache-line (so called 'false sharing').
Separate the producer-published fields from the consumer-published
fields; document the locks relevant to each field.
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
drivers/tty/n_tty.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index adccff8..9b828f0 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -86,28 +86,38 @@
#define NO_ROOM 0
struct n_tty_data {
- unsigned int column;
+ /* producer-published */
+ size_t read_head;
+ size_t canon_head;
+ DECLARE_BITMAP(process_char_map, 256);
+
+ /* private to n_tty_receive_overrun (single-threaded) */
unsigned long overrun_time;
int num_overrun;
+ /* atomic */
unsigned long flags;
+ /* must hold exclusive termios_rwsem to reset these */
unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1;
unsigned char echo_overrun:1;
- DECLARE_BITMAP(process_char_map, 256);
+ /* shared by producer and consumer */
+ char *read_buf;
DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE);
- char *read_buf;
- size_t read_head;
- size_t read_tail;
int minimum_to_wake;
+ /* consumer-published */
+ size_t read_tail;
+
+ /* protected by echo_lock */
unsigned char *echo_buf;
unsigned int echo_pos;
unsigned int echo_cnt;
- size_t canon_head;
+ /* protected by output lock */
+ unsigned int column;
unsigned int canon_column;
struct mutex atomic_read_lock;
--
1.8.1.2
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
