[PATCH] evdev: fix input lag when processing input from output repaint

Chase Douglas chase.douglas at canonical.com
Tue Mar 20 21:36:33 PDT 2012

On 03/20/2012 05:02 PM, Kristian Hoegsberg wrote:
> On Tue, Mar 20, 2012 at 11:54:56AM +0200, Ander Conselvan de Oliveira wrote:
>> When the compositor is in a repaint cycle, input is processed only once
>> per frame. However, a call to evdev_input_device_data() would handle at
>> most 8 events at time. When there was more than 8 events pending for a
>> given frame, input lag would occur. This was most visible with multi
>> touch input.
>> This patch changes the evdev_input_device_data() so that it will handle
>> all the events available in the fd. In order to do that, the fd is put
>> in non-blocking mode, so that it is possible to loop on read and stop
>> on EAGAIN instead of blocking.
> Yikes, ok.  I think the patch is ok, though I'd prefer to make
> wl_event_loop_dispatch() return "number of events dispatched" or maybe
> just 1 if it dispatched any events, and then iterate until it returns
> 0.  Since we already have to do O_NONBLOCK for mtdev, lets just go
> with this (but I'll note for the record that I really don't like that
> aspect of mtdev, and it doesn't have to do that).

I haven't really followed the discussion, but mtdev is fairly small. It
probably wouldn't take too much to fix mtdev to behave correctly,
however that is.

-- Chase

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