Merged vs. User-Only - Inclusive Time
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Merged vs. User-Only - Inclusive Time
Merged vs. User-Only - Exclusive Time
1. Observing Program-OS Interaction Example 1: "Interrupts”(Interrupts induced by large number of icmp pings)
Approx. 25 secs dilation in Total Inclusive Time. Why?
User-Only Inclusive Time View User-Only Exclusive Time View
Approx. 16 secs dilation in MPSP() Exclusive Time. Why?
Application Profile does not tell the whole story!
NAS Parallel Benchmark SP Class W run with and without interrupts
1. Observing Program-OS Interaction Example 1: "Interrupts”(Interrupts induced by large number of icmp pings)
Kernel-Space Time Taken by:
1.do_softirq()
2. schedule()
3. do_IRQ()
4. sys_poll()
5. icmp_rcv()
6. icmp_reply()
Merged Inclusive Time View Merged Exclusive Time View
MPSP excl. time difference only 4 secs.
Excl-time view clearly identifies the culprits.
1. schedule()
2. do_IRQ()
3. icmp_reply()
4. do_softirq()
Pings cause interrupts (do_IRQ). Which in turn handled after interrupt by soft-interrupts (do_softirq). Actual routine is icmp_reply/rcv.
Large number of softirqs causes ksoftirqd to be scheduled-in, causing SP to be scheduled-out.