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

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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