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Peter Anvin" , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, Yongwei Ma , Xiong Zhang , Jim Mattson , Sandipan Das , Zide Chen , Eranian Stephane , Shukla Manali , Nikunj Dadhania References: <20250324173121.1275209-1-mizhang@google.com> <20250324173121.1275209-2-mizhang@google.com> Content-Language: en-US From: "Mi, Dapeng" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/15/2025 6:48 AM, Sean Christopherson wrote: > On Mon, Mar 24, 2025, Mingwei Zhang wrote: >> +/* >> + * Currently invoked at VM creation to >> + * - Check whether there are existing !exclude_guest events of PMU with >> + * PERF_PMU_CAP_MEDIATED_VPMU >> + * - Set nr_mediated_pmu_vms to prevent !exclude_guest event creation on >> + * PMUs with PERF_PMU_CAP_MEDIATED_VPMU >> + * >> + * No impact for the PMU without PERF_PMU_CAP_MEDIATED_VPMU. The perf >> + * still owns all the PMU resources. >> + */ >> +int perf_get_mediated_pmu(void) >> +{ >> + guard(mutex)(&perf_mediated_pmu_mutex); >> + if (atomic_inc_not_zero(&nr_mediated_pmu_vms)) >> + return 0; >> + >> + if (atomic_read(&nr_include_guest_events)) >> + return -EBUSY; >> + >> + atomic_inc(&nr_mediated_pmu_vms); >> + return 0; >> +} >> +EXPORT_SYMBOL_GPL(perf_get_mediated_pmu); > IMO, all of the mediated PMU logic should be guarded with a Kconfig. I strongly > suspect KVM x86 will be the only user for the foreseeable, e.g. arm64 is trending > toward a partioned PMU approach, and subjecting other architectures to the (minor) > overhead associated with e.g. nr_mediated_pmu_vms seems pointless. The other > nicety is that it helps encapsulate the mediated PMU code, which for those of us > that haven't been living and breathing this for the last few months, is immensely > helpful. I'm fine with this. > >> +void perf_put_mediated_pmu(void) > To avoid confusion with perf_put_guest_context() in future patches, I think it > makes sense to go with something like perf_{create,release}_mediated_pmu(). I > actually like the get/put terminology in isolation, but they look weird side-by-side. Agree.