linux-kernel - Re: [PATCH V3 0/8] TopDown metrics support for Icelake

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Date:   Wed, 7 Aug 2019 09:42:01 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     peterz@...radead.org, acme@...nel.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, jolsa@...nel.org, eranian@...gle.com,
        alexander.shishkin@...ux.intel.com, ak@...ux.intel.com
Subject: Re: [PATCH V3 0/8] TopDown metrics support for Icelake

Hi Peter,

Any comments for this series?

Thanks,
Kan

On 7/24/2019 1:17 PM, kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
> 
> Icelake has support for measuring the level 1 TopDown metrics
> directly in hardware. This is implemented by an additional METRICS
> register, and a new Fixed Counter 3 that measures pipeline SLOTS.
> 
> Four TopDown metric events as separate perf events, which map to
> internal METRICS register, are exposed. They are topdown-retiring,
> topdown-bad-spec, topdown-fe-bound and topdown-be-bound.
> Those events do not exist in hardware, but can be allocated by the
> scheduler. The value of TopDown metric events can be calculated by
> multiplying the METRICS (percentage) register with SLOTS fixed counter.
> 
> New in Icelake
> - Do not require generic counters. This allows to collect TopDown always
>    in addition to other events.
> - Measuring TopDown per thread/process instead of only per core
> 
> Limitation
> - To get accurate result and avoid reading the METRICS register multiple
>    times, the TopDown metrics events and SLOTS event have to be in the
>    same group.
> - METRICS and SLOTS registers have to be cleared after each read by SW.
>    That is to prevent the lose of precision and a known side effect of
>    METRICS register.
> - Cannot do sampling read SLOTS and TopDown metric events
> 
> Please refer SDM Vol3, 18.3.9.3 Performance Metrics for the details of
> TopDown metrics.
> 
> Changes since V2:
> - Rebase on top of v5.3-rc1
> 
> Key changes since V1:
> - Remove variables for reg_idx and enabled_events[] array.
>    The reg_idx can be calculated by idx in runtime.
>    Using existing active_mask to replace enabled_events.
> - Choose value 47 for the fixed index of BTS.
> - Support OVF_PERF_METRICS overflow bit in PMI handler
> - Drops the caching mechanism and related variables
>    New mechanism is to update all active slots/metrics events for the
>    first slots/metrics events in a group. For each group reading, it
>    still only read the slots/perf_metrics MSR once
> - Disable PMU for read of topdown events to avoid the NMI issue
> - Move RDPMC support to a separate patch
> - Using event=0x00,umask=0x1X for topdown metrics events
> - Drop the patch which add REMOVE transaction
>    We can indicate x86_pmu_stop() by checking
>    (event && !test_bit(event->hw.idx, cpuc->active_mask)),
>    which is a good place to save the slots/metrics MSR value
> 
> Andi Kleen (2):
>    perf, tools, stat: Support new per thread TopDown metrics
>    perf, tools: Add documentation for topdown metrics
> 
> Kan Liang (6):
>    perf/x86/intel: Set correct mask for TOPDOWN.SLOTS
>    perf/x86/intel: Basic support for metrics counters
>    perf/x86/intel: Support hardware TopDown metrics
>    perf/x86/intel: Support per thread RDPMC TopDown metrics
>    perf/x86/intel: Export TopDown events for Icelake
>    perf/x86/intel: Disable sampling read slots and topdown
> 
>   arch/x86/events/core.c                 |  35 ++-
>   arch/x86/events/intel/core.c           | 362 ++++++++++++++++++++++++-
>   arch/x86/events/perf_event.h           |  33 +++
>   arch/x86/include/asm/msr-index.h       |   3 +
>   arch/x86/include/asm/perf_event.h      |  54 +++-
>   include/linux/perf_event.h             |   3 +
>   tools/perf/Documentation/perf-stat.txt |   9 +-
>   tools/perf/Documentation/topdown.txt   | 223 +++++++++++++++
>   tools/perf/builtin-stat.c              |  24 ++
>   tools/perf/util/stat-shadow.c          |  89 ++++++
>   tools/perf/util/stat.c                 |   4 +
>   tools/perf/util/stat.h                 |   8 +
>   12 files changed, 827 insertions(+), 20 deletions(-)
>   create mode 100644 tools/perf/Documentation/topdown.txt
>