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Date: Sat, 15 May 2021 18:30:15 +0800
From: Liuxiangdong <liuxiangdong5@...wei.com>
To: Like Xu <like.xu@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>,
Paolo Bonzini <pbonzini@...hat.com>
CC: Borislav Petkov <bp@...en8.de>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>, <weijiang.yang@...el.com>,
Kan Liang <kan.liang@...ux.intel.com>, <ak@...ux.intel.com>,
<wei.w.wang@...el.com>, <eranian@...gle.com>,
<linux-kernel@...r.kernel.org>, <x86@...nel.org>,
<kvm@...r.kernel.org>, "Fangyi (Eric)" <eric.fangyi@...wei.com>,
Xiexiangyou <xiexiangyou@...wei.com>
Subject: Re: [PATCH v6 00/16] KVM: x86/pmu: Add *basic* support to enable
guest PEBS via DS
On 2021/5/11 10:41, Like Xu wrote:
> A new kernel cycle has begun, and this version looks promising.
>
> The guest Precise Event Based Sampling (PEBS) feature can provide
> an architectural state of the instruction executed after the guest
> instruction that exactly caused the event. It needs new hardware
> facility only available on Intel Ice Lake Server platforms. This
> patch set enables the basic PEBS feature for KVM guests on ICX.
>
> We can use PEBS feature on the Linux guest like native:
>
> # perf record -e instructions:ppp ./br_instr a
> # perf record -c 100000 -e instructions:pp ./br_instr a
Hi, Like.
Has the qemu patch been modified?
https://lore.kernel.org/kvm/f4dcb068-2ddf-428f-50ad-39f65cad3710@intel.com/
?
> To emulate guest PEBS facility for the above perf usages,
> we need to implement 2 code paths:
>
> 1) Fast path
>
> This is when the host assigned physical PMC has an identical index as
> the virtual PMC (e.g. using physical PMC0 to emulate virtual PMC0).
> This path is used in most common use cases.
>
> 2) Slow path
>
> This is when the host assigned physical PMC has a different index
> from the virtual PMC (e.g. using physical PMC1 to emulate virtual PMC0)
> In this case, KVM needs to rewrite the PEBS records to change the
> applicable counter indexes to the virtual PMC indexes, which would
> otherwise contain the physical counter index written by PEBS facility,
> and switch the counter reset values to the offset corresponding to
> the physical counter indexes in the DS data structure.
>
> The previous version [0] enables both fast path and slow path, which
> seems a bit more complex as the first step. In this patchset, we want
> to start with the fast path to get the basic guest PEBS enabled while
> keeping the slow path disabled. More focused discussion on the slow
> path [1] is planned to be put to another patchset in the next step.
>
> Compared to later versions in subsequent steps, the functionality
> to support host-guest PEBS both enabled and the functionality to
> emulate guest PEBS when the counter is cross-mapped are missing
> in this patch set (neither of these are typical scenarios).
>
> With the basic support, the guest can retrieve the correct PEBS
> information from its own PEBS records on the Ice Lake servers.
> And we expect it should work when migrating to another Ice Lake
> and no regression about host perf is expected.
>
> Here are the results of pebs test from guest/host for same workload:
>
> perf report on guest:
> # Samples: 2K of event 'instructions:ppp', # Event count (approx.): 1473377250
> # Overhead Command Shared Object Symbol
> 57.74% br_instr br_instr [.] lfsr_cond
> 41.40% br_instr br_instr [.] cmp_end
> 0.21% br_instr [kernel.kallsyms] [k] __lock_acquire
>
> perf report on host:
> # Samples: 2K of event 'instructions:ppp', # Event count (approx.): 1462721386
> # Overhead Command Shared Object Symbol
> 57.90% br_instr br_instr [.] lfsr_cond
> 41.95% br_instr br_instr [.] cmp_end
> 0.05% br_instr [kernel.vmlinux] [k] lock_acquire
> Conclusion: the profiling results on the guest are similar tothat on the host.
>
> A minimum guest kernel version may be v5.4 or a backport version
> support Icelake server PEBS.
>
> Please check more details in each commit and feel free to comment.
>
> Previous:
> https://lore.kernel.org/kvm/20210415032016.166201-1-like.xu@linux.intel.com/
>
> [0] https://lore.kernel.org/kvm/20210104131542.495413-1-like.xu@linux.intel.com/
> [1] https://lore.kernel.org/kvm/20210115191113.nktlnmivc3edstiv@two.firstfloor.org/
>
> V5 -> V6 Changelog:
> - Rebased on the latest kvm/queue tree;
> - Fix a git rebase issue (Liuxiangdong);
> - Adjust the patch sequence 06/07 for bisection (Liuxiangdong);
>
> Like Xu (16):
> perf/x86/intel: Add EPT-Friendly PEBS for Ice Lake Server
> perf/x86/intel: Handle guest PEBS overflow PMI for KVM guest
> perf/x86/core: Pass "struct kvm_pmu *" to determine the guest values
> KVM: x86/pmu: Set MSR_IA32_MISC_ENABLE_EMON bit when vPMU is enabled
> KVM: x86/pmu: Introduce the ctrl_mask value for fixed counter
> KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS
> KVM: x86/pmu: Reprogram PEBS event to emulate guest PEBS counter
> KVM: x86/pmu: Add IA32_DS_AREA MSR emulation to support guest DS
> KVM: x86/pmu: Add PEBS_DATA_CFG MSR emulation to support adaptive PEBS
> KVM: x86: Set PEBS_UNAVAIL in IA32_MISC_ENABLE when PEBS is enabled
> KVM: x86/pmu: Adjust precise_ip to emulate Ice Lake guest PDIR counter
> KVM: x86/pmu: Move pmc_speculative_in_use() to arch/x86/kvm/pmu.h
> KVM: x86/pmu: Disable guest PEBS temporarily in two rare situations
> KVM: x86/pmu: Add kvm_pmu_cap to optimize perf_get_x86_pmu_capability
> KVM: x86/cpuid: Refactor host/guest CPU model consistency check
> KVM: x86/pmu: Expose CPUIDs feature bits PDCM, DS, DTES64
>
> arch/x86/events/core.c | 5 +-
> arch/x86/events/intel/core.c | 129 ++++++++++++++++++++++++------
> arch/x86/events/perf_event.h | 5 +-
> arch/x86/include/asm/kvm_host.h | 16 ++++
> arch/x86/include/asm/msr-index.h | 6 ++
> arch/x86/include/asm/perf_event.h | 5 +-
> arch/x86/kvm/cpuid.c | 24 ++----
> arch/x86/kvm/cpuid.h | 5 ++
> arch/x86/kvm/pmu.c | 50 +++++++++---
> arch/x86/kvm/pmu.h | 38 +++++++++
> arch/x86/kvm/vmx/capabilities.h | 26 ++++--
> arch/x86/kvm/vmx/pmu_intel.c | 115 +++++++++++++++++++++-----
> arch/x86/kvm/vmx/vmx.c | 24 +++++-
> arch/x86/kvm/vmx/vmx.h | 2 +-
> arch/x86/kvm/x86.c | 14 ++--
> 15 files changed, 368 insertions(+), 96 deletions(-)
>
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