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Date: Tue, 18 May 2021 20:23:56 +0800
From: Liuxiangdong <liuxiangdong5@...wei.com>
To: Like Xu <like.xu@...ux.intel.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>,
Peter Zijlstra <peterz@...radead.org>,
"Paolo Bonzini" <pbonzini@...hat.com>
Subject: Re: [PATCH v6 00/16] KVM: x86/pmu: Add *basic* support to enable
guest PEBS via DS
On 2021/5/17 14:38, Like Xu wrote:
> Hi xiangdong,
>
> On 2021/5/15 18:30, Liuxiangdong wrote:
>>
>>
>> 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/
>> ?
>
> I think the qemu part still works based on
> 609d7596524ab204ccd71ef42c9eee4c7c338ea4 (tag: v6.0.0).
>
Yes. I applied these two qemu patches to qemu v6.0.0 and this kvm
patches set to latest kvm tree.
I can see pebs flags in Guest(linux 5.11) on the IceLake( Model: 106
Model name: Intel(R) Xeon(R) Platinum 8378A CPU),
and i can use PEBS like this.
#perf record -e instructions:pp
It can work normally.
But there is no sampling when i use "perf record -e events:pp" or just
"perf record" in guest
unless i delete patch 09 and patch 13 from this kvm patches set.
Have you tried "perf record -e events:pp" in this patches set? Does it
work normally?
Thanks!
Xiangdong Liu
> When the LBR qemu patch receives the ACK from the maintainer,
> I will submit PBES qemu support because their changes are very similar.
>
> Please help review this version and
> feel free to add your comments or "Reviewed-by".
>
> Thanks,
> Like Xu
>
>>
>>
>>> 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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