[PATCH libinput 2/2] evdev: ratelimit SYN_DROPPED logging

[Bill Spitzak]

I got the impression the ratelimit object was intended to be a single 
static instance, not per-device. The idea is that if there is a burst of 
these at once they are all from the same device, or due to some 
interaction between them, so you want to limit it all. Also it prevents 
an implementation detail from being in the exposed data structure.

On 11/04/2014 12:35 AM, David Herrmann wrote:
> Use the ratelimit helpers for SYN_DROPPED logging. This guarantees that we
> will still receive SYN_DROPPED log-messages after multiple days of
> runtime, even though there might have been a SYN_DROPPED flood at one
> point in time.
>
> Signed-off-by: David Herrmann <dh.herrmann at gmail.com>
> ---
>   src/evdev.c | 14 +++++++-------
>   src/evdev.h |  4 +---
>   2 files changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/src/evdev.c b/src/evdev.c
> index 3aa87a7..836ce56 100644
> --- a/src/evdev.c
> +++ b/src/evdev.c
> @@ -926,16 +926,14 @@ 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++;
> +			if (ratelimit_test(&device->syn_drop_limit))
>   				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);
> -			}
> +			else if (ratelimit_cutoff(&device->syn_drop_limit))
> +					log_info(libinput, "SYN_DROPPED flood "
> +						 "for \"%s\"\n",
> +						 device->devname);
>
>   			/* send one more sync event so we handle all
>   			   currently pending events before we sync up
> @@ -1296,6 +1294,8 @@ evdev_device_create(struct libinput_seat *seat,
>   	device->scroll.threshold = 5.0; /* Default may be overridden */
>   	device->scroll.direction = 0;
>   	device->dpi = DEFAULT_MOUSE_DPI;
> +	/* at most 5 SYN_DROPPED log-messages per 30s */
> +	device->syn_drop_limit = RATELIMIT_INIT(30ULL * 1000 * 1000, 5);
>
>   	matrix_init_identity(&device->abs.calibration);
>   	matrix_init_identity(&device->abs.usermatrix);
> diff --git a/src/evdev.h b/src/evdev.h
> index 666c8dc..eefbb79 100644
> --- a/src/evdev.h
> +++ b/src/evdev.h
> @@ -137,9 +137,7 @@ struct evdev_device {
>   	} buttons;
>
>   	int dpi; /* HW resolution */
> -	/* The number of times libevdev processes a SYN_DROPPED, so we can
> -	 * stop logging them to avoid flooding the logs. */
> -	int syn_drops_received;
> +	struct ratelimit syn_drop_limit; /* ratelimit for SYN_DROPPED logging */
>   };
>
>   #define EVDEV_UNHANDLED_DEVICE ((struct evdev_device *) 1)
>