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Commit fb7aa03d authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
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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: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f95499c3

drivers/tty/n_tty.c

+15 −6
Original line number Diff line number Diff line
@@ -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;