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Commit 9dfd16dd authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
Browse files

n_tty: Avoid false-sharing echo buffer indices 



Separate the head & commit indices from the tail index to avoid
cache-line contention (so called 'false-sharing') between concurrent
threads.

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 29c7c5ca

drivers/tty/n_tty.c

+4 −5
Original line number Diff line number Diff line
@@ -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;