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SubjectRe: [RFC PATCH] perf_core: provide a kernel-internal interface to get to performance counters
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On Thu, 2009-10-01 at 10:53 +0200, Ingo Molnar wrote:
> i'd suggest you extend perf events with a 'system
> wide' event abstraction, which:
>
> - Enumerates such registered events (via a list)
>
> - Adds a CPU hotplug handler (which clones those events over to a new
> CPU and directs it back to the ring-buffer of the existing event(s)
> [if any])
>
> - Plus a state field that allows the filtering out of stray/premature
> events.
>
> Such an add-on layer/abstraction would sure be useful in other cases as
> well. It might make sense to expose it to user-space and make perf top
> use it by default.

Non-trivial.

Something like this would imply a single output channel for all these
CPUs, and we've already seen that stuffing too many CPUs down one such
channel (using -M) leads to significant performance issues.

Therefore I would strongly argue to let the kernel interface be what it
is and solve this in a userspace library for those who care.

We really cannot sanely support an all-CPUs abstraction without running
into trouble.




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