Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933159Ab0FELLi (ORCPT ); Sat, 5 Jun 2010 07:11:38 -0400 Received: from smtp-out11.han.skanova.net ([195.67.226.200]:34425 "EHLO smtp-out11.han.skanova.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932741Ab0FELLg (ORCPT ); Sat, 5 Jun 2010 07:11:36 -0400 From: "Henrik Rydberg" To: Dmitry Torokhov Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, Jiri Kosina , Mika Kuoppala , Benjamin Tissoires , Rafi Rubin , Henrik Rydberg Subject: [PATCH 1/3] input: evdev: Use multi-reader buffer to save space (rev4) Date: Sat, 5 Jun 2010 13:04:27 +0200 Message-Id: <1275735869-2185-2-git-send-email-rydberg@euromail.se> X-Mailer: git-send-email 1.6.3.3 In-Reply-To: <1275735869-2185-1-git-send-email-rydberg@euromail.se> References: <1275735869-2185-1-git-send-email-rydberg@euromail.se> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4176 Lines: 133 Preparing for larger buffer needs, convert the current per-client circular buffer to a single buffer with multiple clients. Ideally, there should be a mechanism where clients wait during buffer collision only. Meanwhile, let clients take the dev->event_lock, which is already held during buffer writes. Signed-off-by: Henrik Rydberg --- drivers/input/evdev.c | 46 ++++++++++++++++++++++++++-------------------- 1 files changed, 26 insertions(+), 20 deletions(-) diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c index 2ee6c7a..7117589 100644 --- a/drivers/input/evdev.c +++ b/drivers/input/evdev.c @@ -33,13 +33,13 @@ struct evdev { spinlock_t client_lock; /* protects client_list */ struct mutex mutex; struct device dev; + int 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 +48,13 @@ 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, + struct evdev *evdev, 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) + /* sync the reader such that it never becomes empty */ + if (client->tail != evdev->head) + client->head = evdev->head; + if (type == EV_SYN) kill_fasync(&client->fasync, SIGIO, POLL_IN); } @@ -78,14 +73,18 @@ static void evdev_event(struct input_handle *handle, event.code = code; event.value = value; + /* dev->event_lock held */ + evdev->buffer[evdev->head] = event; + evdev->head = (evdev->head + 1) & (EVDEV_BUFFER_SIZE - 1); + rcu_read_lock(); client = rcu_dereference(evdev->grab); if (client) - evdev_pass_event(client, &event); + evdev_sync_event(client, evdev, type); else list_for_each_entry_rcu(client, &evdev->client_list, node) - evdev_pass_event(client, &event); + evdev_sync_event(client, evdev, type); rcu_read_unlock(); @@ -269,7 +268,6 @@ 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); @@ -325,19 +323,27 @@ static ssize_t evdev_write(struct file *file, const char __user *buffer, } static int evdev_fetch_next_event(struct evdev_client *client, + struct evdev *evdev, struct input_event *event) { + struct input_dev *dev = evdev->handle.dev; int have_event; - spin_lock_irq(&client->buffer_lock); + /* + * FIXME: taking event_lock protects against reentrant fops + * reads and provides sufficient buffer locking. However, + * clients should not block writes, and having multiple clients + * waiting for each other is suboptimal. + */ + spin_lock_irq(&dev->event_lock); have_event = client->head != client->tail; if (have_event) { - *event = client->buffer[client->tail++]; + *event = evdev->buffer[client->tail++]; client->tail &= EVDEV_BUFFER_SIZE - 1; } - spin_unlock_irq(&client->buffer_lock); + spin_unlock_irq(&dev->event_lock); return have_event; } @@ -366,7 +372,7 @@ 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(client, evdev, &event)) { if (input_event_to_user(buffer + retval, &event)) return -EFAULT; -- 1.6.3.3 -- 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/