How to speed up sending event to /dev/input/eventX in Linux?

Question

I am working on an embedded Linux system with kernel-5.10.24, and I want to send events to system by writing to /dev/input/eventX.
With my testing of sendevent (sendevent.c), the event injecting is NOT as quick as from real hardware.
I think it might be because the overhead to write each event to /dev/intput/eventX from user space to kernel.
So I am wondering if there is a quick way for user space to send events as quick as possible?

Thanks,

Answer 1

The slowness comes from followings.

1. fork process to run sendevent command;
2. open /dev/input/eventX - in sendevent_main()
3. write event data to above file - in sendevent_main();
4. close the file - in sendevent_main().

I got it faster by changing the sendevent_main() as follows.

1. open /dev/input/eventX;
2. open the file with a list of events;
3. create a loop and do followings
   3.1 read the event one by one from above file
   3.2 write the event one by one to `/dev/input/eventX'
4. close files.

So in above changes, the event read and write is done in a loop without overhead ofopen and close for each event as before.

With this change, it is much faster to send event to /dev/input/eventX.
But it brings in another problem, some events' behavior is NOT correct as expected. Is it sending event too fast to be handled by application?

I am still checking and changing the code, such as add usleep(10000) between event sending. But it goes back to the original slowness.

Struggling.....