linux-kernel - Re: [PATCH] KVM: x86/pmu: Fix HW_REF_CPU_CYCLES event pseudo-encoding in intel_arch

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Date:   Mon, 18 Jan 2021 12:40:39 +0800
From:   "Xu, Like" <like.xu@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Stephane Eranian <eranian@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Like Xu <like.xu@...ux.intel.com>
Subject: Re: [PATCH] KVM: x86/pmu: Fix HW_REF_CPU_CYCLES event pseudo-encoding
 in intel_arch_events[]

On 2021/1/16 1:30, Sean Christopherson wrote:
> On Fri, Jan 15, 2021, Like Xu wrote:
>> Ping ?
>>
>> On 2020/12/30 16:19, Like Xu wrote:
>>> The HW_REF_CPU_CYCLES event on the fixed counter 2 is pseudo-encoded as
>>> 0x0300 in the intel_perfmon_event_map[]. Correct its usage.
>>>
>>> Fixes: 62079d8a4312 ("KVM: PMU: add proper support for fixed counter 2")
>>> Signed-off-by: Like Xu <like.xu@...ux.intel.com>
> Reviewed-by: Sean Christopherson <seanjc@...gle.com>
thx.
>
>>> ---
>>>    arch/x86/kvm/vmx/pmu_intel.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
>>> index a886a47daebd..013e8d253dfa 100644
>>> --- a/arch/x86/kvm/vmx/pmu_intel.c
>>> +++ b/arch/x86/kvm/vmx/pmu_intel.c
>>> @@ -29,7 +29,7 @@ static struct kvm_event_hw_type_mapping intel_arch_events[] = {
>>>    	[4] = { 0x2e, 0x41, PERF_COUNT_HW_CACHE_MISSES },
>>>    	[5] = { 0xc4, 0x00, PERF_COUNT_HW_BRANCH_INSTRUCTIONS },
>>>    	[6] = { 0xc5, 0x00, PERF_COUNT_HW_BRANCH_MISSES },
>>> -	[7] = { 0x00, 0x30, PERF_COUNT_HW_REF_CPU_CYCLES },
>>> +	[7] = { 0x00, 0x03, PERF_COUNT_HW_REF_CPU_CYCLES },
> In a follow up patch, would it be sane/appropriate to define these magic numbers
> in asm/perf_event.h and share them between intel_perfmon_event_map and
> intel_arch_events?  Without this patch, it's not at all obvious that these are
> intended to align with the Core (arch?) event definitions.

The asm/perf_event.h is x86 generic and svm has a amd_perfmon_event_map.

How about adding an interface similar to perf_get_x86_pmu_capability()
so that we can use magic numbers directly from the host perf ?
(it looks we may have a performance drop, compared to static array)

---
thx, likexu

>
>>>    };
>>>    /* mapping between fixed pmc index and intel_arch_events array */