Q: How to update the running time?

For more information about Linux programming and kernel, see the following. I compiled a program to test the real-time scheduling capability of Linux. I used the Linux timer and the real-time process of the signal generation cycle to set the process attributes in the signal processing function, including the running time of the process exec_time,
Then add the following in the kernel schedule:
Run_time = now-prev-> timestamp;
If (prev-> exec_time-runtime) <0)
Prev-> exec_time = 0;
Else
Prev-> exectime-= runtime;

Call rt_getexec () to read the remaining running time, but the read time is not changed, which is equal to the set value.