Re: [PATCH V7 00/18] KVM: x86/pmu: Add *basic* support to enable guest PEBS via DS

Zhu, Lingshan
2021-06-25T09:46:25Z

On 6/25/2021 5:40 PM, Liuxiangdong wrote:
>
>
> On 2021/6/22 17:42, Zhu Lingshan 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 feature for KVM guests on ICX.
>>
>> We can use PEBS feature on the Linux guest like native:
>>
>>     # echo 0 > /proc/sys/kernel/watchdog (on the host)
>
> Only on the host?
> I cannot use pebs unless try with "echo 0 > /proc/sys/kernel/watchdog"
> both on the host and guest on ICX.
Hi Xiangdong

I guess you may run into the "cross-map" case(slow path below), so I
think you can disable them both in host and guest to make PEBS work.

Thanks
>
>>     # 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.
>>
>> 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/20210511024214.280733-1-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/
>>
>>
>> V6 -> V7 Changelog:
>> - Fix conditions order and call x86_pmu_handle_guest_pebs()
>> unconditionally; (PeterZ)
>> - Add a new patch to make all that perf_guest_cbs stuff suck less;
>> (PeterZ)
>> - Document IA32_MISC_ENABLE[7] that that behavior matches bare metal;
>> (Sean & Venkatesh)
>> - Update commit message for fixed counter mask refactoring;(PeterZ)
>> - Clarifying comments about {.host and .guest} for
>> intel_guest_get_msrs(); (PeterZ)
>> - Add pebs_capable to store valid PEBS_COUNTER_MASK value; (PeterZ)
>> - Add more comments for perf's precise_ip field; (Andi & PeterZ)
>> - Refactor perf_overflow_handler_t and make it more legible; (PeterZ)
>> - Use "(unsigned long)cpuc->ds" instead of
>> __this_cpu_read(cpu_hw_events.ds); (PeterZ)
>> - Keep using "(struct kvm_pmu *)data" to follow K&R; (Andi)
>>
>> Like Xu (17):
>>    perf/core: Use static_call to optimize perf_guest_info_callbacks
>>    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: Adjust precise_ip to emulate Ice Lake guest PDIR
>> 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: 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
>>
>> Peter Zijlstra (Intel) (1):
>>    x86/perf/core: Add pebs_capable to store valid PEBS_COUNTER_MASK
>> value
>>
>>   arch/arm/kernel/perf_callchain.c   |  16 +--
>>   arch/arm64/kernel/perf_callchain.c |  29 +++--
>>   arch/arm64/kvm/perf.c              |  22 ++--
>>   arch/csky/kernel/perf_callchain.c  |   4 +-
>>   arch/nds32/kernel/perf_event_cpu.c |  16 +--
>>   arch/riscv/kernel/perf_callchain.c |   4 +-
>>   arch/x86/events/core.c             |  43 ++++++--
>>   arch/x86/events/intel/core.c       | 165 +++++++++++++++++++++++------
>>   arch/x86/events/perf_event.h       |   6 +-
>>   arch/x86/include/asm/kvm_host.h    |  18 +++-
>>   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                 |  60 ++++++++---
>>   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                 |  51 +++++----
>>   arch/x86/xen/pmu.c                 |  33 +++---
>>   include/linux/perf_event.h         |  12 ++-
>>   kernel/events/core.c               |   9 ++
>>   24 files changed, 544 insertions(+), 189 deletions(-)
>>
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