Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754209Ab3C0Ltl (ORCPT ); Wed, 27 Mar 2013 07:49:41 -0400 Received: from mailout01.c08.mtsvc.net ([205.186.168.189]:54558 "EHLO mailout01.c08.mtsvc.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753924Ab3C0LsN (ORCPT ); Wed, 27 Mar 2013 07:48:13 -0400 From: Peter Hurley To: Greg Kroah-Hartman , Jiri Slaby Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Min Zhang , Ilya Zykov , Peter Hurley Subject: [PATCH v2 18/18] n_tty: Separate buffer indices to prevent cache-line sharing Date: Wed, 27 Mar 2013 07:44:08 -0400 Message-Id: <1364384648-6636-19-git-send-email-peter@hurleysoftware.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1364384648-6636-1-git-send-email-peter@hurleysoftware.com> References: <1363724513-15604-1-git-send-email-peter@hurleysoftware.com> <1364384648-6636-1-git-send-email-peter@hurleysoftware.com> X-Authenticated-User: 125194 peter@hurleysoftware.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1831 Lines: 68 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 --- 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; -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/