linux-kernel - Re: [PATCH v2 2/6] KVM: x86/pmu: Refactoring find_arch_event() to pmc_perf_hw

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Date:   Mon, 14 Feb 2022 15:44:34 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Like Xu <like.xu.linux@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, David Dunn <daviddunn@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Kim Phillips <kim.phillips@....com>,
        Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH v2 2/6] KVM: x86/pmu: Refactoring find_arch_event() to
 pmc_perf_hw_id()



On 11-Feb-22 11:46 PM, Jim Mattson wrote:
> On Fri, Feb 11, 2022 at 1:56 AM Ravi Bangoria <ravi.bangoria@....com> wrote:
>>
>>
>>
>> On 10-Feb-22 4:58 PM, Like Xu wrote:
>>> cc Kim and Ravi to help confirm more details about this change.
>>>
>>> On 10/2/2022 3:30 am, Jim Mattson wrote:
>>>> By the way, the following events from amd_event_mapping[] are not
>>>> listed in the Milan PPR:
>>>> { 0x7d, 0x07, PERF_COUNT_HW_CACHE_REFERENCES }
>>>> { 0x7e, 0x07, PERF_COUNT_HW_CACHE_MISSES }
>>>> { 0xd0, 0x00, PERF_COUNT_HW_STALLED_CYCLES_FRONTEND }
>>>> { 0xd1, 0x00, PERF_COUNT_HW_STALLED_CYCLES_BACKEND }
>>>>
>>>> Perhaps we should build a table based on amd_f17h_perfmon_event_map[]
>>>> for newer AMD processors?
>>
>> I think Like's other patch series to unify event mapping across kvm
>> and host will fix it. No?
>> https://lore.kernel.org/lkml/20220117085307.93030-4-likexu@tencent.com
> 
> Yes, that should fix it. But why do we even bother? What is the
> downside of using PERF_TYPE_RAW all of the time?

There are few places where PERF_TYPE_HARDWARE and PERF_TYPE_RAW are treated
differently. Ex, x86_pmu_event_init(), perf_init_event(). So I think it makes
sense to keep using PERF_TYPE_HARDWARE for generalized events?

Ravi