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n_tty: Avoid false-sharing echo buffer indices

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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>
This commit is contained in:
Peter Hurley 2013-06-15 10:04:29 -04:00 committed by Greg Kroah-Hartman
parent 29c7c5ca36
commit 9dfd16ddea
1 changed files with 4 additions and 5 deletions
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9
drivers/tty/n_tty.c
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@ -90,6 +90,8 @@ struct n_tty_data {
/* 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 @@ struct n_tty_data {
/* 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;