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Date: Sat, 2 Jan 2016 20:39:21 -0800
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Aniroop Mathur <a.mathur@...sung.com>
Cc: linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
aniroop.mathur@...il.com, Aniroop Mathur <a.mathur@...sung.com>,
Benjamin Tissoires <benjamin.tissoires@...il.com>,
David Herrmann <dh.herrmann@...il.com>,
Peter Hutterer <peter.hutterer@...-t.net>,
Henrik Rydberg <rydberg@...math.org>
Subject: Re: [PATCH] Input: evdev - drop partial events after emptying the
buffer
On Thu, Dec 31, 2015 at 03:36:47AM +0530, Aniroop Mathur wrote:
> This patch introduces concept to drop partial events in evdev handler
> itself after emptying the buffer which are dropped by all evdev
> clients in userspace after SYN_DROPPED occurs.
> This in turn saves space of partial events in evdev handler buffer
> and reduces evdev client reading requests.
Let's add a few people who write consumer code to see if this is
something that they consider useful.
>
> Signed-off-by: Aniroop Mathur <a.mathur@...sung.com>
> ---
> drivers/input/evdev.c | 49 +++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 45 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> index e9ae3d5..e7b612e 100644
> --- a/drivers/input/evdev.c
> +++ b/drivers/input/evdev.c
> @@ -58,6 +58,7 @@ struct evdev_client {
> struct list_head node;
> unsigned int clk_type;
> bool revoked;
> + bool drop_pevent; /* specifies whether partial events need to be dropped */
> unsigned long *evmasks[EV_CNT];
> unsigned int bufsize;
> struct input_event buffer[];
> @@ -192,6 +193,7 @@ static int evdev_set_clk_type(struct evdev_client *client, unsigned int clkid)
> {
> unsigned long flags;
> unsigned int clk_type;
> + struct input_event *ev;
>
> switch (clkid) {
>
> @@ -218,6 +220,17 @@ static int evdev_set_clk_type(struct evdev_client *client, unsigned int clkid)
> spin_lock_irqsave(&client->buffer_lock, flags);
>
> if (client->head != client->tail) {
> +
> + /*
> + * Set drop_pevent to true if last event packet is
> + * not stored completely in buffer.
> + */
> + client->head--;
> + client->head &= client->bufsize - 1;
> + ev = &client->buffer[client->head];
> + if (!(ev->type == EV_SYN && ev->code == SYN_REPORT))
> + client->drop_pevent = true;
> +
> client->packet_head = client->head = client->tail;
> __evdev_queue_syn_dropped(client);
> }
> @@ -228,31 +241,51 @@ static int evdev_set_clk_type(struct evdev_client *client, unsigned int clkid)
> return 0;
> }
>
> -static void __pass_event(struct evdev_client *client,
> +static bool __pass_event(struct evdev_client *client,
> const struct input_event *event)
> {
> + struct input_event *prev_ev;
> +
> client->buffer[client->head++] = *event;
> client->head &= client->bufsize - 1;
>
> if (unlikely(client->head == client->tail)) {
> /*
> - * This effectively "drops" all unconsumed events, leaving
> - * EV_SYN/SYN_DROPPED plus the newest event in the queue.
> + * This effectively "drops" all unconsumed events, storing
> + * EV_SYN/SYN_DROPPED and the newest event in the queue but
> + * only if it is not part of partial packet.
> + * Set drop_pevent to true if last event packet is not stored
> + * completely in buffer and set to false if SYN_REPORT occurs.
> */
> +
> client->tail = (client->head - 2) & (client->bufsize - 1);
>
> + prev_ev = &client->buffer[client->tail];
> + if (!(prev_ev->type == EV_SYN && prev_ev->code == SYN_REPORT)) {
> + client->drop_pevent = true;
> + client->head--;
> + client->head &= client->bufsize - 1;
> + }
> +
> client->buffer[client->tail].time = event->time;
> client->buffer[client->tail].type = EV_SYN;
> client->buffer[client->tail].code = SYN_DROPPED;
> client->buffer[client->tail].value = 0;
>
> client->packet_head = client->tail;
> +
> + if (event->type == EV_SYN && event->code == SYN_REPORT) {
> + client->drop_pevent = false;
> + return true;
> + }
> }
>
> if (event->type == EV_SYN && event->code == SYN_REPORT) {
> client->packet_head = client->head;
> kill_fasync(&client->fasync, SIGIO, POLL_IN);
> }
> +
> + return false;
> }
>
> static void evdev_pass_values(struct evdev_client *client,
> @@ -284,10 +317,18 @@ static void evdev_pass_values(struct evdev_client *client,
> wakeup = true;
> }
>
> + /* drop partial events until SYN_REPORT occurs */
> + if (client->drop_pevent) {
> + if (v->type == EV_SYN && v->code == SYN_REPORT)
> + client->drop_pevent = false;
> + continue;
> + }
> +
> event.type = v->type;
> event.code = v->code;
> event.value = v->value;
> - __pass_event(client, &event);
> + if (__pass_event(client, &event))
> + wakeup = false;
> }
>
> spin_unlock(&client->buffer_lock);
> --
> 2.6.2
>
--
Dmitry
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