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Message-ID: <86f43058-a51a-42c7-4d75-564f0e8eef04@intel.com>
Date:   Tue, 10 Jan 2023 08:35:48 +0200
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Subject: Re: [RFC 0/4] perf tool: Fix non-".text" symbol resolution for kernel
 modules
To:     Ravi Bangoria <ravi.bangoria@amd.com>, acme@kernel.org
Cc:     jolsa@kernel.org, namhyung@kernel.org, irogers@google.com,
        kan.liang@linux.intel.com, peterz@infradead.org,
        mark.rutland@arm.com, mingo@redhat.com,
        alexander.shishkin@linux.intel.com, james.clark@arm.com,
        german.gomez@arm.com, leo.yan@linaro.org,
        alexey.v.bayduraev@linux.intel.com,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        sandipan.das@amd.com, ananth.narayan@amd.com,
        santosh.shukla@amd.com
References: <20230110055859.685-1-ravi.bangoria@amd.com>
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From:   Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
 Business Identity Code: 0357606 - 4, Domiciled in Helsinki
In-Reply-To: <20230110055859.685-1-ravi.bangoria@amd.com>
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On 10/01/23 07:58, Ravi Bangoria wrote:
> Kernel module elf contains executable code in non-".text" sections as
> well, for ex: ".noinstr.text". Plus, kernel module's memory layout
> differs from it's binary layout because .ko elf does not contain
> program header table.

Have you looked at using perf record --kcore option.

> 
> Perf tries to solve it by creating special maps for allocated (SHF_ALLOC)
> elf sections, but perf uses elf addresses for map address range and thus
> these special maps remains unused because no real ip falls into their
> address range.
> 
> Solve this by preparing section specific special maps using addresses
> provided by sysfs /sys/module/.../sections/. Also save these details in
> PERF_RECORD_KMOD_SEC_MAP format in perf.data which can be consumed at
> perf-report time.
> 
> Without patchset:
> 
>   # perf record -a -c 5000000
>   # perf report
>   Overhead  Command          Shared Object           Symbol
>     13.20%  qemu-system-x86  [unknown]               [.] 0x00005557527b1973
>      6.58%  qemu-system-x86  [kvm_amd]               [k] 0x00000000000151e6
>      6.36%  qemu-system-x86  [kernel.vmlinux]        [k] native_load_gdt
>      6.21%  qemu-system-x86  [kernel.vmlinux]        [k] native_load_tr_desc
>      4.71%  qemu-system-x86  [kvm]                   [k] vcpu_run
>      4.52%  qemu-system-x86  [kvm_amd]               [k] svm_vcpu_run
>      3.50%  qemu-system-x86  [kvm]                   [k] kvm_cpuid
>      2.09%  qemu-system-x86  [kvm]                   [k] kvm_pmu_trigger_event
>      1.98%  qemu-system-x86  [kvm_amd]               [k] 0x0000000000015171
>      1.05%  qemu-system-x86  [kvm_amd]               [k] svm_handle_exit
>      1.04%  qemu-system-x86  [kvm_amd]               [k] 0x00000000000151e2
>      0.94%  qemu-system-x86  [kvm_amd]               [k] 0x0000000000015174
> 
>   Same perf.data with kallsyms:
> 
>   # perf report --kallsyms=/proc/kallsyms
>   Overhead  Command          Shared Object           Symbol
>     14.22%  qemu-system-x86  [kvm_amd]               [k] __svm_vcpu_run
>     13.20%  qemu-system-x86  [unknown]               [.] 0x00005557527b1973
>      6.36%  qemu-system-x86  [kernel.vmlinux]        [k] native_load_gdt
>      6.21%  qemu-system-x86  [kernel.vmlinux]        [k] native_load_tr_desc
>      4.71%  qemu-system-x86  [kvm]                   [k] vcpu_run
>      4.52%  qemu-system-x86  [kvm_amd]               [k] svm_vcpu_run
>      3.50%  qemu-system-x86  [kvm]                   [k] kvm_cpuid
>      2.09%  qemu-system-x86  [kvm]                   [k] kvm_pmu_trigger_event
>      1.05%  qemu-system-x86  [kvm_amd]               [k] svm_handle_exit
> 
> With patchset:
> 
>   # perf record -a -c 5000000
>   # perf report
>   Overhead  Command          Shared Object           Symbol
>     13.44%  qemu-system-x86  [kvm-amd].noinstr.text  [k] __svm_vcpu_run
>     13.25%  qemu-system-x86  [unknown]               [.] 0x000055f4c6563973
>      7.13%  qemu-system-x86  [kernel.vmlinux]        [k] native_load_gdt
>      6.00%  qemu-system-x86  [kernel.vmlinux]        [k] native_load_tr_desc
>      5.13%  qemu-system-x86  [kvm_amd]               [k] svm_vcpu_run
>      4.83%  qemu-system-x86  [kvm]                   [k] vcpu_run
>      3.65%  qemu-system-x86  [kvm]                   [k] kvm_cpuid
> 
>   Same perf.data with kallsyms:
> 
>   # perf report --kallsyms=/proc/kallsyms
>   Overhead  Command          Shared Object       Symbol
>     13.44%  qemu-system-x86  [kernel.vmlinux]    [k] __svm_vcpu_run
>     13.25%  qemu-system-x86  [unknown]           [.] 0x000055f4c6563973
>      7.13%  qemu-system-x86  [kernel.vmlinux]    [k] native_load_gdt
>      6.00%  qemu-system-x86  [kernel.vmlinux]    [k] native_load_tr_desc
>      5.13%  qemu-system-x86  [kernel.vmlinux]    [k] svm_vcpu_run
>      4.83%  qemu-system-x86  [kernel.vmlinux]    [k] vcpu_run
>      3.65%  qemu-system-x86  [kernel.vmlinux]    [k] kvm_cpuid
> 
> This is an RFC only series. TODOs:
>  - I'm just recording module path in PERF_RECORD_KMOD_SEC_MAP. It's very
>    much possible that, at perf report time, a module file exists at the
>    same path but it's internal layout is different. I think I need to add
>    some buildid check. Any ideas?
>  - I've enabled host perf-record/report only. It doesn't work for guest
>    modules because host does not have access to guest sysfs. I'm yet to
>    figure out how to fix it. May be we can add --guest-mod-sysfs option.
>    Any ideas?
>  - Also, I'm currently assuming that module files are not compressed.
>  - I've seen perf build failures when compiling with NO_LIBELF=1.
>  - I've seen perf report not honoring --kallsyms in certain conditions.
> 
> Prepared on top of acme/perf/core (69b41ac87e4a6)
> 
> Ravi Bangoria (4):
>   perf tool: Simplify machine__create_modules() a bit
>   perf tool: Refactor perf_event__synthesize_modules()
>   perf tool: Introduce PERF_RECORD_KMOD_SEC_MAP
>   perf tool: Fix non-".text" symbol resolution for kernel modules
> 
>  tools/lib/perf/Documentation/libperf.txt |   1 +
>  tools/lib/perf/include/perf/event.h      |  25 +++
>  tools/perf/builtin-annotate.c            |   1 +
>  tools/perf/builtin-c2c.c                 |   1 +
>  tools/perf/builtin-diff.c                |   1 +
>  tools/perf/builtin-inject.c              |   1 +
>  tools/perf/builtin-kmem.c                |   1 +
>  tools/perf/builtin-mem.c                 |   1 +
>  tools/perf/builtin-record.c              |  14 ++
>  tools/perf/builtin-report.c              |   1 +
>  tools/perf/builtin-script.c              |  13 ++
>  tools/perf/builtin-trace.c               |   1 +
>  tools/perf/util/build-id.c               |   1 +
>  tools/perf/util/data-convert-bt.c        |   1 +
>  tools/perf/util/data-convert-json.c      |   1 +
>  tools/perf/util/event.c                  |  22 ++
>  tools/perf/util/event.h                  |   5 +
>  tools/perf/util/machine.c                | 268 ++++++++++++++++++++++-
>  tools/perf/util/machine.h                |   2 +
>  tools/perf/util/map.c                    |   1 +
>  tools/perf/util/map.h                    |   4 +
>  tools/perf/util/session.c                |  17 ++
>  tools/perf/util/symbol-elf.c             |   9 +-
>  tools/perf/util/symbol.c                 |   2 +-
>  tools/perf/util/synthetic-events.c       | 136 +++++++++---
>  tools/perf/util/tool.h                   |   3 +-
>  26 files changed, 494 insertions(+), 39 deletions(-)
>