From fb7aa03db605e4f0b9a62cd4c77177c2596edd95 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Sat, 15 Jun 2013 09:14:30 -0400 Subject: [PATCH] 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 Signed-off-by: Greg Kroah-Hartman --- 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 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; -- 2.11.0