Chapter 4 - DSpace at Waseda University

Chapter 5
latency. Figure 5.5 shows the model of the HRTimer latency. When a local apic interrupt
occurs software interrupts are occurred after an interrupt handler takes action. If HRTimer
expired, it is stopped by kernel_timer_itimer_expired.
Figure 5.5 Hrtimer latency model
We define the HRTimer latency model as follows:
�
�
lapic
T : The time from occurring HRTimer hardware interrupt to occurring hardirq
handler to be expired.
softirq
T : The time from occurring softirq to until processing softirq handler
expired
� . T : The time from after softirq handler to until expired HRTimer.
When there is delay in timer, following formula is required to check how delay was
occurred.
� Formula (1):
time
T Means a time of the HRTimer’s execution which is the all of time
for HRTimer processing time and HRTimer latency.
� Formula (2): Checking whether time latency occurred or not by comparing
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tick
HRT to