linux-kernel - Re: [PATCH 3/3] KVM: x86/pmu: Segregate Intel and AMD specific logic

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Date:   Thu, 3 Mar 2022 21:55:16 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Like Xu <like.xu.linux@...il.com>, seanjc@...gle.com,
        dave.hansen@...ux.intel.com, peterz@...radead.org,
        alexander.shishkin@...ux.intel.com, eranian@...gle.com,
        daviddunn@...gle.com, ak@...ux.intel.com,
        kan.liang@...ux.intel.com, x86@...nel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, kim.phillips@....com,
        santosh.shukla@....com,
        "Paolo Bonzini - Distinguished Engineer (kernel-recipes.org) (KVM HoF)" 
        <pbonzini@...hat.com>, Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH 3/3] KVM: x86/pmu: Segregate Intel and AMD specific logic



On 03-Mar-22 10:08 AM, Jim Mattson wrote:
> On Mon, Feb 21, 2022 at 2:02 AM Ravi Bangoria <ravi.bangoria@....com> wrote:
>>
>>
>>
>> On 21-Feb-22 1:27 PM, Like Xu wrote:
>>> On 21/2/2022 3:31 pm, Ravi Bangoria wrote:
>>>>   void reprogram_counter(struct kvm_pmu *pmu, int pmc_idx)
>>>>   {
>>>>       struct kvm_pmc *pmc = kvm_x86_ops.pmu_ops->pmc_idx_to_pmc(pmu, pmc_idx);
>>>> +    bool is_intel = !strncmp(kvm_x86_ops.name, "kvm_intel", 9);
>>>
>>> How about using guest_cpuid_is_intel(vcpu)
>>
>> Yeah, that's better then strncmp().
>>
>>> directly in the reprogram_gp_counter() ?
>>
>> We need this flag in reprogram_fixed_counter() as well.
> 
> Explicit "is_intel" checks in any form seem clumsy,

Indeed. However introducing arch specific callback for such tiny
logic seemed overkill to me. So thought to just do it this way.

> since we have
> already put some effort into abstracting away the implementation
> differences in struct kvm_pmu. It seems like these differences could
> be handled by adding three masks to that structure: the "raw event
> mask" (i.e. event selector and unit mask), the hsw_in_tx mask, and the
> hsw_in_tx_checkpointed mask.

struct kvm_pmu is arch independent. You mean struct kvm_pmu_ops?

> 
> These changes should also be coordinated with Like's series that
> eliminates all of the PERF_TYPE_HARDWARE nonsense.

I'll rebase this on Like's patch series.

Thanks,
Ravi