[PATCH libinput] evdev: Log evdev event queue overflows

[Bill Spitzak]

I can't imagine any way this static variable will mess up with multiple 
threads. At worst not exactly 10 messages will be printed but that seems 
really harmless. Every processor writes to memory a number larger than 
it read, so eventually every processor will see a number >= 10 even if 
there was absolutely no synchronization.

On 10/28/2014 12:18 PM, Derek Foreman wrote:
> On 28/10/14 03:20 AM, Ran Benita wrote:
>> On Mon, Oct 27, 2014 at 09:26:39AM -0500, Derek Foreman 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 | 10 ++++++++++
>>>   1 file changed, 10 insertions(+)
>>>
>>> diff --git a/src/evdev.c b/src/evdev.c
>>> index 1b4ce10..c786537 100644
>>> --- a/src/evdev.c
>>> +++ b/src/evdev.c
>>> @@ -912,6 +912,7 @@ evdev_sync_device(struct evdev_device *device)
>>>   static void
>>>   evdev_device_dispatch(void *data)
>>>   {
>>> +	static int overflows = 0;
>>
>> Does libinput allow static variables? Usually when there's a library
>> context, it should be possible to use the library from multiple threads,
>> if they use different contexts.
>>
>> So maybe this counter should be inside `device` instead of static?
>
> I'm not sure libinput is completely thread safe, but that's an easy
> change to make.
>
> I'd like to put it in struct libinput to preserve the current behaviour
> - but that puts an evdev specific wart in an otherwise generic structure.
>
> Any objections?
>
>> Ran
>>
>>>   	struct evdev_device *device = data;
>>>   	struct libinput *libinput = device->base.seat->libinput;
>>>   	struct input_event ev;
>>> @@ -924,6 +925,15 @@ evdev_device_dispatch(void *data)
>>>   		rc = libevdev_next_event(device->evdev,
>>>   					 LIBEVDEV_READ_FLAG_NORMAL, &ev);
>>>   		if (rc == LIBEVDEV_READ_STATUS_SYNC) {
>>> +			if (overflows < 10) {
>>> +				overflows++;
>>> +				log_info(libinput, "Kernel evdev event queue "
>>> +					 "overflow for %s\n", device->devname);
>>> +				if (overflows == 10)
>>> +					log_info(libinput, "No longer logging "
>>> +						 "evdev event queue overflows\n");
>>> +			}
>>> +
>>>   			/* send one more sync event so we handle all
>>>   			   currently pending events before we sync up
>>>   			   to the current state */
>>> --
>>> 2.1.1
>>>
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