Sender: Paolo Bonzini <paolo.bonzini@gmail.com>
Message-ID: <9edd8c8a-26ee-9615-4b64-0ddeab1e9184@redhat.com>
Date:   Thu, 9 Dec 2021 20:24:34 +0100
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Subject: Re: [PATCH v2 2/6] KVM: x86/pmu: Refactoring find_arch_event() to
 pmc_perf_hw_id()
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To:     Jim Mattson <jmattson@google.com>,
        Like Xu <like.xu.linux@gmail.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Like Xu <likexu@tencent.com>
References: <20211130074221.93635-1-likexu@tencent.com>
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 <CALMp9eRaZBftkaFsmfH8V519QdSGKTORp0OAZ2WaNi3f9X=tng@mail.gmail.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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On 12/9/21 04:52, Jim Mattson wrote:
> Why don't we just use PERF_TYPE_RAW for guest counters all of the
> time? What is the advantage of matching entries in a table so that we
> can use PERF_TYPE_HARDWARE?

In theory it's so that hosts without support for architectural PMU 
events can map the architectural PMU events to their own.  In practice, 
we can probably return early from intel_pmu_refresh if the host does not 
support X86_FEATURE_ARCH_PERFMON, because only the oldest Pentium 4 
toasters^Wprocessors probably have VMX but lack architectural PMU.

Paolo