Time Signal Latency

Time Signal Latency

It takes time for the kernel to deliver the SIGALRM that notifies your program at the end of the interval. (The issue of signal latency in general is discussed under "Signal Delivery and Latency".) The signal latency is less for SIGALRM than for other signals, since the kernel initiates a scheduling cycle immediately after the timer interrupt, without waiting for the end of a fixed time slice. When the program is running or ready to run, in a CPU that has been restricted and isolated (as discussed in Chapter 6), the latency is fairly short and consistent from one signal to the next. (Even so, it is not advisable to use a repeating itimer as the time base for a real-time program). Under less favorable conditions, signal latency can be variable and sometimes lengthy (tens of milliseconds) relative to a fast timer frequency.