[PATCH 4/4] input: evdev: only wake poll on EV_SYN

From: Jeff Brown
Date: Tue Mar 22 2011 - 21:04:51 EST

On SMP systems, it is possible for an evdev client blocked on poll()
to wake up and read events from the evdev ring buffer at the same
rate as they are enqueued. This can result in high CPU usage,
particularly for MT devices, because the client ends up reading
events one at a time instead of reading complete packets. This patch
ensures that the client only wakes from poll() when a complete packet
is ready to be read.

Signed-off-by: jeffbrown@xxxxxxxxxxx
drivers/input/evdev.c | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index 203ed70..7b6770d 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -73,7 +73,7 @@ static void evdev_pass_event(struct evdev_client *client,

- if (event->type == EV_SYN)
+ if (event->type == EV_SYN && event->code != SYN_MT_REPORT)
kill_fasync(&client->fasync, SIGIO, POLL_IN);

@@ -103,7 +103,8 @@ static void evdev_event(struct input_handle *handle,


- wake_up_interruptible(&evdev->wait);
+ if (type == EV_SYN && code != SYN_MT_REPORT)
+ wake_up_interruptible(&evdev->wait);

static int evdev_fasync(int fd, struct file *file, int on)

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