Messages in this thread | | | Subject | Re: [PATCH v4 00/16] KVM: x86/pmu: Add basic support to enable Guest PEBS via DS | From | "Xu, Like" <> | Date | Tue, 6 Apr 2021 11:19:22 +0800 |
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Hi all, do we have any comments on this patch set?
On 2021/3/29 13:41, Like Xu wrote: > 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 via DS 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 > > 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. > > Please check more details in each commit and feel free to comment. > > Previous: > [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/ > > v3->v4 Changelog: > - Update this cover letter and propose a new upstream plan; > [PERF] > - Drop check host DS and move handler to handle_pmi_common(); > - Pass "struct kvm_pmu *" to intel_guest_get_msrs(); > - Propose new assignment logic for perf_guest_switch_msr(); > - Introduce x86_pmu.pebs_vmx for future capability maintenance; > [KVM] > - Add kvm_pmu_cap to optimize perf_get_x86_pmu_capability; > - Raising PEBS PMI only when OVF_BIT 62 is not set; > - Make vmx_icl_pebs_cpu specific for PEBS-PDIR emulation; > - Fix a bug for fixed_ctr_ctrl_mask; > - Add two minor refactoring patches for reuse; > > Like Xu (16): > perf/x86/intel: Add x86_pmu.pebs_vmx for Ice Lake Servers > 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: Reprogram guest PEBS event to emulate guest PEBS counter > KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS > KVM: x86/pmu: Add IA32_DS_AREA MSR emulation to manage guest DS buffer > 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 before vm-entry in two cases > 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 | 93 +++++++++++++++++++++++--- > 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 | 49 ++++++++++---- > arch/x86/kvm/pmu.h | 37 +++++++++++ > arch/x86/kvm/vmx/capabilities.h | 26 ++++++-- > arch/x86/kvm/vmx/pmu_intel.c | 105 ++++++++++++++++++++++++------ > arch/x86/kvm/vmx/vmx.c | 25 ++++++- > arch/x86/kvm/vmx/vmx.h | 2 +- > arch/x86/kvm/x86.c | 14 ++-- > 15 files changed, 339 insertions(+), 78 deletions(-) >
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