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.