Date:   Thu, 12 Dec 2019 08:47:26 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     peterz@...radead.org, acme@...hat.com, mingo@...nel.org,
        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 V5 RESEND 00/14] TopDown metrics support for Icelake


Hi Peter,

Could you please take a look at the patch set? If there is anything 
needs to be improved, please let me know.

Thanks,
Kan

On 12/3/2019 9:11 AM, 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.
> 
> 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
> 
> For the Ice Lake implementation of performance metrics, the values in
> PERF_METRICS MSR are derived from fixed counter 3. Software should start
> both registers, PERF_METRICS and fixed counter 3, from zero.
> Additionally, software is recommended to periodically clear both
> registers in order to maintain accurate measurements. The latter is
> required for certain scenarios that involve sampling metrics at high
> rates. Software should always write fixed counter 3 before write to
> PERF_METRICS.
> 
> IA32_PERF_GLOBAL_STATUS. OVF_PERF_METRICS[48]: If this bit is set,
> it indicates that some PERF_METRICS-related counter has overflowed and
> a PMI is triggered. Software has to synchronize, e.g. re-start,
> PERF_METRICS as well as fixed counter 3. Otherwise, PERF_METRICS may
> return invalid values.
> 
> 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.
> - 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 V4:
> - Add description regarding to event-code naming for fixed counters
> - Fix add_nr_metric_event().
>    For leader event, we have to take the accepted metrics events into
>    account.
>    For sibling event, it doesn't need to count accepted metrics events
>    again.
> - Remove is_first_topdown_event_in_group().
>    Force slots in topdown group. Only update topdown events with slots
>    event.
> - Re-use last_period and period_left for saved_metric and saved_slots.
> 
> Changes since V3:
> - Separate fixed counter3 definition patch
> - Separate BTS index patch
> - Apply Peter's cleanup patch
> - Fix the name of perf capabilities for perf METRICS
> - Apply patch for mul_u64_u32_div() x86_64 implementation
> - Fix unconditionally allows collecting 4 extra events
> - Add patch to clean up NMI handler by naming global status bit
> - Add patch to reuse event_base_rdpmc for RDPMC userspace support
> 
> 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 (12):
>    perf/x86/intel: Introduce the fourth fixed counter
>    perf/x86/intel: Set correct mask for TOPDOWN.SLOTS
>    perf/x86/intel: Move BTS index to 47
>    perf/x86/intel: Basic support for metrics counters
>    perf/x86/intel: Fix the name of perf capabilities for perf METRICS
>    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
>    perf/x86/intel: Name global status bit in NMI handler
>    perf/x86: Use event_base_rdpmc for RDPMC userspace support
>    perf, tools, stat: Check Topdown Metric group
> 
>   arch/x86/events/core.c                 |  86 +++++-
>   arch/x86/events/intel/core.c           | 399 ++++++++++++++++++++++---
>   arch/x86/events/perf_event.h           |  57 +++-
>   arch/x86/include/asm/msr-index.h       |   3 +
>   arch/x86/include/asm/perf_event.h      |  60 +++-
>   include/linux/perf_event.h             |  29 +-
>   tools/perf/Documentation/perf-stat.txt |   9 +-
>   tools/perf/Documentation/topdown.txt   | 235 +++++++++++++++
>   tools/perf/builtin-stat.c              |  97 ++++++
>   tools/perf/util/stat-shadow.c          |  89 ++++++
>   tools/perf/util/stat.c                 |   4 +
>   tools/perf/util/stat.h                 |   8 +
>   12 files changed, 1007 insertions(+), 69 deletions(-)
>   create mode 100644 tools/perf/Documentation/topdown.txt
> 

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