Re: [PATCH v5 0/8] perf/amd: Zen4 IBS extensions support (tool changes)

[Liang, Kan]

On 5/31/2022 11:26 PM, Ravi Bangoria wrote:
> Kernel side of changes have already been applied to linus/master
> (except amd-ibs.h header). This series contains perf tool changes.
>
> Kan, I don't have any machine with heterogeneou cpus. It would be
> helpful if you can check HEADER_PMU_CAPS on Intel ADL machine.

I tried the patch 2-5 on a hybrid machine. I didn't see any regression 
with perf report --header-only option.

Without the patch 2-5,
# perf report --header-only | grep capabilities
# cpu_core pmu capabilities: branches=32, max_precise=3, 
pmu_name=alderlake_hybrid
# cpu_atom pmu capabilities: branches=32, max_precise=3, 
pmu_name=alderlake_hybrid

With the patch 2-5,
# ./perf report --header-only | grep capabilities
# cpu_core pmu capabilities: branches=32, max_precise=3, 
pmu_name=alderlake_hybrid
# cpu_atom pmu capabilities: branches=32, max_precise=3, 
pmu_name=alderlake_hybrid


Thanks,
Kan


> v4: https://lore.kernel.org/lkml/20220523033945.1612-1-ravi.bangoria@xxxxxxx
> v4->v5:
>   - Replace HEADER_HYBRID_CPU_PMU_CAPS with HEADER_PMU_CAPS instead of
>     adding new header HEADER_PMU_CAPS. Special care is taken by writing
>     hybrid cpu pmu caps first in the header to make sure old perf tool
>     does not break.
>   - Store HEADER_CPU_PMU_CAPS capabilities in an array instead of single
>     string separated by NULL.
>   - Include "cpu" pmu while searching for capabilities in perf_env.
>   - Rebase on acme/perf/core (9dde6cadb92b5)
>
> Original cover letter:
>
> IBS support has been enhanced with two new features in upcoming uarch:
> 1. DataSrc extension and 2. L3 Miss Filtering capability. Both are
> indicated by CPUID_Fn8000001B_EAX bit 11.
>
> DataSrc extension provides additional data source details for tagged
> load/store operations. Add support for these new bits in perf report/
> script raw-dump.
>
> IBS L3 miss filtering works by tagging an instruction on IBS counter
> overflow and generating an NMI if the tagged instruction causes an L3
> miss. Samples without an L3 miss are discarded and counter is reset
> with random value (between 1-15 for fetch pmu and 1-127 for op pmu).
> This helps in reducing sampling overhead when user is interested only
> in such samples. One of the use case of such filtered samples is to
> feed data to page-migration daemon in tiered memory systems.
>
> Add support for L3 miss filtering in IBS driver via new pmu attribute
> "l3missonly". Example usage:
>
>    # perf record -a -e ibs_op/l3missonly=1/ --raw-samples sleep 5
>    # perf report -D
>
> Some important points to keep in mind while using L3 miss filtering:
> 1. Hw internally reset sampling period when tagged instruction does
>     not cause L3 miss. But there is no way to reconstruct aggregated
>     sampling period when this happens.
> 2. L3 miss is not the actual event being counted. Rather, IBS will
>     count fetch, cycles or uOps depending on the configuration. Thus
>     sampling period have no direct connection to L3 misses.
>
> 1st causes sampling period skew. Thus, I've added warning message at
> perf record:
>
>    # perf record -c 10000 -C 0 -e ibs_op/l3missonly=1/
>    WARNING: Hw internally resets sampling period when L3 Miss Filtering is enabled
>    and tagged operation does not cause L3 Miss. This causes sampling period skew.
>
> User can configure smaller sampling period to get more samples while
> using l3missonly.
>
>
> Ravi Bangoria (8):
>    perf record ibs: Warn about sampling period skew
>    perf tool: Parse pmu caps sysfs only once
>    perf headers: Pass "cpu" pmu name while printing caps
>    perf headers: Store pmu caps in an array of strings
>    perf headers: Record non-cpu pmu capabilities
>    perf/x86/ibs: Add new IBS register bits into header
>    perf tool ibs: Sync amd ibs header file
>    perf script ibs: Support new IBS bits in raw trace dump
>
>   arch/x86/include/asm/amd-ibs.h                |  16 +-
>   tools/arch/x86/include/asm/amd-ibs.h          |  16 +-
>   .../Documentation/perf.data-file-format.txt   |  10 +-
>   tools/perf/arch/x86/util/evsel.c              |  49 +++++
>   tools/perf/builtin-inject.c                   |   2 +-
>   tools/perf/util/amd-sample-raw.c              |  68 +++++-
>   tools/perf/util/env.c                         |  62 +++++-
>   tools/perf/util/env.h                         |  14 +-
>   tools/perf/util/evsel.c                       |   7 +
>   tools/perf/util/evsel.h                       |   1 +
>   tools/perf/util/header.c                      | 196 ++++++++++--------
>   tools/perf/util/header.h                      |   2 +-
>   tools/perf/util/pmu.c                         |  15 +-
>   tools/perf/util/pmu.h                         |   2 +
>   14 files changed, 333 insertions(+), 127 deletions(-)