[PATCH 18/18] n_tty: Separate buffer indices to prevent cache-line sharing
From: Peter Hurley <hidden>
Date: 2013-03-19 20:45:21
Also in:
lkml
Subsystem:
the rest, tty layer and serial drivers · Maintainers:
Linus Torvalds, Greg Kroah-Hartman, Jiri Slaby
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 <redacted> --- 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;
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1.8.1.2