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authorPeter Hurley <peter@hurleysoftware.com>2013-06-15 09:14:30 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-07-23 16:43:02 -0700
commitfb7aa03db605e4f0b9a62cd4c77177c2596edd95 (patch)
tree503946923a498b938aa849457310ceedaefbd806 /drivers/tty/n_tty.c
parentf95499c3030fe1bfad57745f2db1959c5b43dca8 (diff)
downloadblackbird-op-linux-fb7aa03db605e4f0b9a62cd4c77177c2596edd95.tar.gz
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n_tty: Separate buffer indices to prevent cache-line sharing
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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/n_tty.c')
-rw-r--r--drivers/tty/n_tty.c21
1 files changed, 15 insertions, 6 deletions
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index a6eea30d0911..d0c8805d8131 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;
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