Chapter 4 - DSpace at Waseda University

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Chapter 5
Figure 5.11 is the data showing the part where HRTimer latency occurred. According to the
result of AL, events such as net_socket_sending, net_dev_xmit, and mm_page_alloc have the
occurred a lot. These events were operated before the HRTimer event (HRTIMER_SOFTIRQ)
was processed and according to the analysis of the kernel source, these events have higher
priority than softriq of HRTimer.
Figure 5.12 shows the result analyzed based on event logs is Figure 5.11. Figure 5.12 shows
how HRTimer analyzes its latency. In the process of executing, between each softirq handler
execution, HRTimer softirq (HRTIMER_SOFTIRQ) is executed. We can find that
run_hrtimer_softirq() occurred after net_dev_xmit (NET_TX_SOFTIRQ) and mm_page_alloc
(BLOCK_SOFTIRQ) that is higher priority than HRTimer softirq.
Figure 5.12: One of the reasons of HRTimer latency
Therefore, Figure 5.13 shows process of interrupt in timeline. When softriq with high
priority is in progress, softriq with low priority cannot be executed. After the high priority
softriq is finished, the low priority (HRTimer softriq) is executed.