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SubjectRe: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods

* Ingo Molnar <mingo@elte.hu> wrote:

> The GUP based method is pretty generic though - and can be used on
> other architectures as well. It's not as fast as direct access
> though.

Another question is: your patch switches over all normal exceptions
from IRET to hand-unroll+RET.

It would be really nice to benchmark it (via 'perf stat' for example
;-) whether that's a slowdown or a speedup.

If it's a slowdown then the decision is easy: we dont want this, we
want to push the overhead into the sampling code, away from common
codepaths.

[ If on the other hand it's a speedup of a few cycles then we have
the problem of me suddenly liking this patch a whole lot more ;-) ]

Ingo


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