Re: [PATCH v6 00/16] KVM: x86/pmu: Add *basic* support to enable guest PEBS via DS

[Like Xu <like.xu@linux.intel.com>]

On 2021/5/19 9:44, Liuxiangdong wrote:
> 
> 
> On 2021/5/18 20:40, Xu, Like wrote:
>> On 2021/5/18 20:23, Liuxiangdong wrote:
>>>
>>>
>>> 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.
>>>
>>>
>>
>> With patch 9 and 13, does the basic counter sampling still work ?
>> You may retry w/ "echo 0 > /proc/sys/kernel/watchdog" on the host and guest.
>>
> 
> In fact, I didn't use "echo 0 > /proc/sys/kernel/watchdog" when I tried 
> PEBS patches V3 on Icelake.
> Why should we use it now?  What does it have to do with sampling?

In the recent patch sets, we disable the guest PEBS when the guest
PEBS counter is cross mapped to a host PEBS counter with a
different index.

When we use the watchdog feature on the Intel platforms,
it may takes a cycle hw counter on the host and it may cause
the guest PEBS counter temporarily disabled if it's cross mapped.

Check patch 0013 for more details.

> 
> Thanks!
> 
>>> Have you tried "perf record -e events:pp" in this patches set? Does it 
>>> work normally?
>>
>> All my PEBS testcases passed. You may dump guest msr traces from your 
>> testcase with me.
>>
>>>
>>>
>>>
>>> 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(-)
>>>>>>
>>>>
>>>
>>
>