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

[Peter Hutterer]

On Mon, Nov 03, 2014 at 11:49:12AM +0100, David Herrmann wrote:
> 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.

good idea, let's do that.

Cheers,
   Peter

> >                         /* 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