How much time is required ARM controller to attend the ISR ???

[AnupB]

I know this is a very basic question, but I want to know to decide whether the polling method is better or the interrupt method is better for time-critical applications.

Kindly help me ...

[waclawek.jan]

The exact answer depends on many many factors. This has been discussed here many times - search.

The best you can do is an experiment - set up an EXTI interrupt, toggle a pin in it, and observe the delay between input and output signal using oscilloscope/logic analyzer. Come back to discuss results. Don't forget to tell us details of your setup.

JW

[KnarfB]

+1

You may also start reading a book. Joseph Yiu "The Definitive Guide..." comes to my mind.

[TDK]

The others are correct, but generally in the tens of cycles.