[RFC] [PATCH] perf, x86: Add PERF_COUNT_HW_NMI_WATCHDOG event

[Cyrill Gorcunov]

Because of Netburst HW restriction we can't move events arbitrary
between counters and this makes 'perf top' unable to run if nmi-watchdog
is running (since both uses PERF_COUNT_HW_CPU_CYCLES but such event is
bound to run on a few counters only). So as a workaround we could count that named
non-sleeping ticks (as oprofile does) and both perf top and nmi-watchdog would co-exsist
without conflicts but kernel needs to know about such specifics -- so PERF_COUNT_HW_NMI_WATCHDOG
event is introduced. This event is an alias of PERF_COUNT_HW_CPU_CYCLES for non-P4 x86
architecture so nothing much changed I think.

Please review, I might be missing something. Also comments on idea is quite welcome since
it touches ABI part.

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