Only treat the main event's period as CPU time for clock events

[antiguru]

Without context-switch records, samply import writes each main-event sample's period into threadCPUDelta as nanoseconds, whatever the event. For perf record -e cycles, this puts cycle counts into the CPU graph as if they were time.

The period now becomes the CPU delta only when the main event is cpu-clock or task-clock. Other main events get a CPU delta of 0.

This changes the Firefox Profiler's CPU graph for imports of non-clock events without context switches: it shows no CPU data instead of wrong values. Imports with context switches and samply record are unchanged. The profile interval is unchanged in all cases.

cpu-clock and task-clock events could not be recorded on the test machine ("Bad event name"), so the clock branch is covered by the unit test only.

Posted by Claude Code.

🤖 Generated with Claude Code

https://claude.ai/code/session_016aEc8uf7GZbHQHXmoX8o2k