lkml.org 
[lkml]   [2013]   [Jun]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v4 18/24] n_tty: Separate buffer indices to prevent cache-line sharing
Date
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@hurleysoftware.com>
---
drivers/tty/n_tty.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index a6eea30..d0c8805 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -82,29 +82,38 @@
#endif

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;

/* non-atomic */
bool no_room;

+ /* 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


\
 
 \ /
  Last update: 2013-06-15 16:01    [W:1.176 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site