perf reordering software events leading to "input corruption" errors

[andikleen]

Some perf versions a4c7d7c502b935f around 6.3 reorder software events, printing WARNING: events were regrouped to match PMU This breaks toplev.

There's a fix pending for upstream perf that fixes it.

In some cases it can be avoid with --tune "KEEP_UNREF = True"

In toplev it could be avoided by not generating dummy events, not using emulation-faults to separate identical events (but use --no-merge instead) and adding software etc. events always at the end. This would need some restructuring in the scheduler.

[andikleen]

There were multiple problems here:

• "slots" not being the first in the group lead to "events were regrouped". This is now fixed in toplev. It always puts slots first.
• perf between 6.3 and 6.4 had a bug where it reordered all software events and some other events. This cannot be worked around in toplev, but is now fixed in upstream perf (in 6.5+). toplev now gives a message pointing to upstream perf.