Figure 2.5 shows the situation where the handler is executed in the kernel. Again, the arriving message triggers an interrupt and forces control flow into the kernel. The kernel receives the message into a buffer and then simply calls the appropriate handler. The handler does its processing and sends its two messages. A return from interrupt leads back into user mode where the interrupted application resumes.
Figure 2.5: Mapped Network Interface, Handler in Kernel:
An arriving message interrupts the currently running
process. The kernel receives the message into a buffer in
main memory and calls the handler without a context switch.
The handler executes and sends its two messages. A return from
interrupt resumes execution of the original user application.
Since the network interface is accessible from
user mode, no savings are possible by executing the handler in
the kernel. However, a context switch to the handler and a trap
to restore the original context can be avoided. The saved time is:
