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Message-ID: <41821a66-8db1-42f1-85d6-fde67a8c072e@linux.intel.com>
Date: Thu, 15 May 2025 13:09:28 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>,
Mingwei Zhang <mizhang@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>, Liang@...gle.com,
Kan <kan.liang@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
Yongwei Ma <yongwei.ma@...el.com>,
Xiong Zhang <xiong.y.zhang@...ux.intel.com>,
Jim Mattson <jmattson@...gle.com>, Sandipan Das <sandipan.das@....com>,
Zide Chen <zide.chen@...el.com>, Eranian Stephane <eranian@...gle.com>,
Shukla Manali <Manali.Shukla@....com>,
Nikunj Dadhania <nikunj.dadhania@....com>
Subject: Re: [PATCH v4 22/38] KVM: x86/pmu: Optimize intel/amd_pmu_refresh()
helpers
On 5/15/2025 8:37 AM, Sean Christopherson wrote:
> This is not an optimization in any sane interpretation of that word.
Yes, maybe clean up or bug fix is more accurate.
>
> On Mon, Mar 24, 2025, Mingwei Zhang wrote:
>> From: Dapeng Mi <dapeng1.mi@...ux.intel.com>
>>
>> Currently pmu->global_ctrl is initialized in the common kvm_pmu_refresh()
>> helper since both Intel and AMD CPUs set enable bits for all GP counters
>> for PERF_GLOBAL_CTRL MSR. But it may be not the best place to initialize
>> pmu->global_ctrl. Strictly speaking, pmu->global_ctrl is vendor specific
> And? There's mounds of KVM code that show it's very, very easy to manage
> global_ctrl in common code.
The original intention is to put all initialization code into a same place,
which looks more easily to maintain. But if you don't like it. would drop
the change.
>
>> and there are lots of global_ctrl related processing in
>> intel/amd_pmu_refresh() helpers, so better handle them in same place.
>> Thus move pmu->global_ctrl initialization into intel/amd_pmu_refresh()
>> helpers.
>>
>> Besides, intel_pmu_refresh() doesn't handle global_ctrl_rsvd and
>> global_status_rsvd properly and fix it.
> Really? You mention a bug fix in passing, and squash it into an opinionated
> refactoring that is advertised as "optimizations" without even stating what the
> bug is? C'mon.
Sorry not clearly to describe the issue. global_ctrl_rsvd and
global_status_rsvd should be updated only when pmu->verion >=2, but the
original code doesn't.
>
>> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
>> Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
>> ---
>> arch/x86/kvm/pmu.c | 10 -------
>> arch/x86/kvm/svm/pmu.c | 14 +++++++--
>> arch/x86/kvm/vmx/pmu_intel.c | 55 ++++++++++++++++++------------------
>> 3 files changed, 39 insertions(+), 40 deletions(-)
>>
>> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
>> index 4e8cefcce7ab..2ac4c039de8b 100644
>> --- a/arch/x86/kvm/pmu.c
>> +++ b/arch/x86/kvm/pmu.c
>> @@ -843,16 +843,6 @@ void kvm_pmu_refresh(struct kvm_vcpu *vcpu)
>> return;
>>
>> kvm_pmu_call(refresh)(vcpu);
>> -
>> - /*
>> - * At RESET, both Intel and AMD CPUs set all enable bits for general
>> - * purpose counters in IA32_PERF_GLOBAL_CTRL (so that software that
>> - * was written for v1 PMUs don't unknowingly leave GP counters disabled
>> - * in the global controls). Emulate that behavior when refreshing the
>> - * PMU so that userspace doesn't need to manually set PERF_GLOBAL_CTRL.
>> - */
>> - if (kvm_pmu_has_perf_global_ctrl(pmu) && pmu->nr_arch_gp_counters)
>> - pmu->global_ctrl = GENMASK_ULL(pmu->nr_arch_gp_counters - 1, 0);
> Absolutely not, this code stays where it is.
Sure.
>
>> }
>>
>> void kvm_pmu_init(struct kvm_vcpu *vcpu)
>> diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
>> index 153972e944eb..eba086ef5eca 100644
>> --- a/arch/x86/kvm/svm/pmu.c
>> +++ b/arch/x86/kvm/svm/pmu.c
>> @@ -198,12 +198,20 @@ static void __amd_pmu_refresh(struct kvm_vcpu *vcpu)
>> pmu->nr_arch_gp_counters = min_t(unsigned int, pmu->nr_arch_gp_counters,
>> kvm_pmu_cap.num_counters_gp);
>>
>> - if (pmu->version > 1) {
>> - pmu->global_ctrl_rsvd = ~((1ull << pmu->nr_arch_gp_counters) - 1);
>> + if (kvm_pmu_cap.version > 1) {
> It's not just global_ctrl. PEBS and the fixed counters also depend on v2+ (the
> SDM contradicts itself; KVM's ABI is that they're v2+).
>
>> + /*
>> + * At RESET, AMD CPUs set all enable bits for general purpose counters in
>> + * IA32_PERF_GLOBAL_CTRL (so that software that was written for v1 PMUs
>> + * don't unknowingly leave GP counters disabled in the global controls).
>> + * Emulate that behavior when refreshing the PMU so that userspace doesn't
>> + * need to manually set PERF_GLOBAL_CTRL.
>> + */
>> + pmu->global_ctrl = BIT_ULL(pmu->nr_arch_gp_counters) - 1;
>> + pmu->global_ctrl_rsvd = ~pmu->global_ctrl;
>> pmu->global_status_rsvd = pmu->global_ctrl_rsvd;
>> }
>>
>> - pmu->counter_bitmask[KVM_PMC_GP] = ((u64)1 << 48) - 1;
>> + pmu->counter_bitmask[KVM_PMC_GP] = BIT_ULL(48) - 1;
> I like these cleanups, but they too belong in a separate patch.
Sure.
>
>> pmu->reserved_bits = 0xfffffff000280000ull;
>> pmu->raw_event_mask = AMD64_RAW_EVENT_MASK;
>> /* not applicable to AMD; but clean them to prevent any fall out */
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