Re: [PATCH] KVM: x86/pmu: Do not accidentally create BTS events

Woodhouse, David
2025-12-01T14:45:23Z

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On Mon, 2025-12-01 at 16:23 +0200, Fernand Sieber wrote
> Perf considers the combination of PERF_COUNT_HW_BRANCH_INSTRUCTIONS with
> a sample_period of 1 a special case and handles this as a BTS event (see
> intel_pmu_has_bts_period()) -- a deviation from the usual semantic,
> where the sample_period represents the amount of branch instructions to
> encounter before the overflow handler is invoked.

That's kind of awful, and seems to be the real underlying cause of the KVM
issue. Can we kill it with fire? Peter?

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