[PATCH libinput v2] evdev: Log evdev event queue overflows

[David Herrmann]

Hi

On Wed, Oct 29, 2014 at 3:56 PM, Derek Foreman <derekf at osg.samsung.com> wrote:
> Log a message when the kernel event queue overflows and events are dropped.
> After 10 messages logging stops to avoid flooding the logs if the condition
> is persistent.
> ---
>  src/evdev.c | 11 +++++++++++
>  src/evdev.h |  4 ++++
>  2 files changed, 15 insertions(+)
>
> diff --git a/src/evdev.c b/src/evdev.c
> index 1b4ce10..9026f5c 100644
> --- a/src/evdev.c
> +++ b/src/evdev.c
> @@ -924,6 +924,17 @@ evdev_device_dispatch(void *data)
>                 rc = libevdev_next_event(device->evdev,
>                                          LIBEVDEV_READ_FLAG_NORMAL, &ev);
>                 if (rc == LIBEVDEV_READ_STATUS_SYNC) {
> +                       if (device->syn_drops_received < 10) {
> +                               device->syn_drops_received++;
> +                               log_info(libinput, "SYN_DROPPED event from "
> +                                        "\"%s\" - some input events have "
> +                                        "been lost.\n", device->devname);
> +                               if (device->syn_drops_received == 10)
> +                                       log_info(libinput, "No longer logging "
> +                                                "SYN_DROPPED events for "
> +                                                "\"%s\"\n", device->devname);
> +                       }
> +

I really appreciate those log-messages, but can we use rate-limiting
here, rather than a per-device counter? I mean, my compositor usually
runs for multiple days, or even weeks. I really don't want it to stop
reporting SYN_DROPPED events just because it got 100 of those during
startup (or something similar).

Something like this:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/lib/ratelimit.c

I can prep a patch if you want.

Thanks
David

>                         /* send one more sync event so we handle all
>                            currently pending events before we sync up
>                            to the current state */
> diff --git a/src/evdev.h b/src/evdev.h
> index c0d6577..9e84623 100644
> --- a/src/evdev.h
> +++ b/src/evdev.h
> @@ -135,6 +135,10 @@ struct evdev_device {
>                 /* Checks if buttons are down and commits the setting */
>                 void (*change_to_left_handed)(struct evdev_device *device);
>         } buttons;
> +
> +       /* The number of times libevdev processes a SYN_DROPPED, so we can
> +        * stop logging them to avoid flooding the logs. */
> +       int syn_drops_received;
>  };
>
>  #define EVDEV_UNHANDLED_DEVICE ((struct evdev_device *) 1)
> --
> 2.1.1
>
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