Chapter 4 - DSpace at Waseda University

Chapter 2
� To count time accurately.
� To manage the deadline
The Linux kernel makes timer function operate by using timer interrupts periodically.
Especially, the function to manage the time limit is useful. For instance, it is effective to use
in re-sending for networks, re-executing for non-responded devices, polling process for the
device which cannot make interruption.
There are mainly two types of Linux timer.
� Global timer
� To manage system time.
� To make interrupt periodically.
� Alarm function.
� CPU local timer
� To execute for certain CPU.
� To occur in each CPU periodically.
� Acknowledge the interrupt on local APIC.
In Figure 2.3, it is the sequence to execute local timer interruption. Generally, if a local timer
interrupt occurs then a local timer soft interrupt are executed. If the local timer interrupt
occurs the interrupt handler is executed. And then, the local timer soft interrupt occurred and
soft interrupt hander is running.
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