From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Henrik Rydberg" Subject: [PATCH 1/3] input: evdev: use multi-reader buffer to save space (rev2) Date: Sat, 29 May 2010 17:57:42 +0200 Message-ID: <1275148664-6238-2-git-send-email-rydberg@euromail.se> References: <1275148664-6238-1-git-send-email-rydberg@euromail.se> Return-path: Received: from ch-smtp02.sth.basefarm.net ([80.76.149.213]:37663 "EHLO ch-smtp02.sth.basefarm.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757328Ab0E2P6T (ORCPT ); Sat, 29 May 2010 11:58:19 -0400 In-Reply-To: <1275148664-6238-1-git-send-email-rydberg@euromail.se> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Dmitry Torokhov Cc: linux-input@vger.kernel.org, Jiri Kosina , Mika Kuoppala , Benjamin Tissoires , Rafi Rubin , Henrik Rydberg Preparing for larger buffer needs, convert the current per-client circular buffer to a single buffer with multiple clients. Use a lock-less mechanism where clients wait during buffer collision only. Signed-off-by: Henrik Rydberg --- drivers/input/evdev.c | 74 +++++++++++++++++++++++++++++------------------- 1 files changed, 45 insertions(+), 29 deletions(-) diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c index 2ee6c7a..9cbed21 100644 --- a/drivers/input/evdev.c +++ b/drivers/input/evdev.c @@ -33,13 +33,14 @@ struct evdev { spinlock_t client_lock; /* protects client_list */ struct mutex mutex; struct device dev; + int head; + int next_head; + struct input_event buffer[EVDEV_BUFFER_SIZE]; }; struct evdev_client { - struct input_event buffer[EVDEV_BUFFER_SIZE]; int head; int tail; - spinlock_t buffer_lock; /* protects access to buffer, head and tail */ struct fasync_struct *fasync; struct evdev *evdev; struct list_head node; @@ -48,18 +49,11 @@ struct evdev_client { static struct evdev *evdev_table[EVDEV_MINORS]; static DEFINE_MUTEX(evdev_table_mutex); -static void evdev_pass_event(struct evdev_client *client, - struct input_event *event) +static inline void evdev_sync_event(struct evdev_client *client, + int head, int type) { - /* - * Interrupts are disabled, just acquire the lock - */ - spin_lock(&client->buffer_lock); - client->buffer[client->head++] = *event; - client->head &= EVDEV_BUFFER_SIZE - 1; - spin_unlock(&client->buffer_lock); - - if (event->type == EV_SYN) + client->head = head; + if (type == EV_SYN) kill_fasync(&client->fasync, SIGIO, POLL_IN); } @@ -78,14 +72,22 @@ static void evdev_event(struct input_handle *handle, event.code = code; event.value = value; + /* lock-less write, interrupts disabled locally */ + evdev->next_head = (evdev->head + 1) & (EVDEV_BUFFER_SIZE - 1); + smp_wmb(); + evdev->buffer[evdev->head] = event; + smp_wmb(); + evdev->head = evdev->next_head; + smp_wmb(); + rcu_read_lock(); client = rcu_dereference(evdev->grab); if (client) - evdev_pass_event(client, &event); + evdev_sync_event(client, evdev->head, type); else list_for_each_entry_rcu(client, &evdev->client_list, node) - evdev_pass_event(client, &event); + evdev_sync_event(client, evdev->head, type); rcu_read_unlock(); @@ -269,7 +271,6 @@ static int evdev_open(struct inode *inode, struct file *file) goto err_put_evdev; } - spin_lock_init(&client->buffer_lock); client->evdev = evdev; evdev_attach_client(evdev, client); @@ -324,22 +325,37 @@ static ssize_t evdev_write(struct file *file, const char __user *buffer, return retval; } -static int evdev_fetch_next_event(struct evdev_client *client, +static inline bool write_overlaps_read(int head, int next_head, int tail) +{ + if (next_head < head) + return tail >= head || tail < next_head; + else + return tail >= head && tail < next_head; +} + +static int evdev_fetch_next_event(struct evdev *evdev, + struct evdev_client *client, struct input_event *event) { - int have_event; + int head, next_head; - spin_lock_irq(&client->buffer_lock); + if (client->head == client->tail) + return 0; - have_event = client->head != client->tail; - if (have_event) { - *event = client->buffer[client->tail++]; - client->tail &= EVDEV_BUFFER_SIZE - 1; + repeat: + head = evdev->head; + smp_rmb(); + *event = evdev->buffer[client->tail]; + smp_rmb(); + next_head = evdev->next_head; + smp_rmb(); + if (unlikely(write_overlaps_read(head, next_head, client->tail))) { + cpu_relax(); + goto repeat; } - spin_unlock_irq(&client->buffer_lock); - - return have_event; + client->tail = (client->tail + 1) & (EVDEV_BUFFER_SIZE - 1); + return 1; } static ssize_t evdev_read(struct file *file, char __user *buffer, @@ -366,7 +382,7 @@ static ssize_t evdev_read(struct file *file, char __user *buffer, return -ENODEV; while (retval + input_event_size() <= count && - evdev_fetch_next_event(client, &event)) { + evdev_fetch_next_event(evdev, client, &event)) { if (input_event_to_user(buffer + retval, &event)) return -EFAULT; -- 1.6.3.3