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n_tty: Separate buffer indices to prevent cache-line sharing

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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>
This commit is contained in:
Peter Hurley 2013-06-15 09:14:30 -04:00 committed by Greg Kroah-Hartman
parent f95499c303
commit fb7aa03db6
1 changed files with 15 additions and 6 deletions
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21
drivers/tty/n_tty.c
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@ -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;