Re: [RFC PATCH v1 0/4] HiSilicon Performance Monitor Control Unit

[Jie Zhan <zhanjie9@hisilicon.com>]

Please can anyone have a look at this PMCU patchset and provide some 
comments?

It is much related to the ARM PMU.

We are looking forward to the feedback.

Any relevant comments/questions, with respect to software or hardware 
design, use cases, coding, are welcome.

Kind regards,

Jie


On 06/02/2023 14:51, Jie Zhan wrote:
> HiSilicon Performance Monitor Control Unit (PMCU) is a device that offloads
> PMU accesses from CPUs, handling the configuration, event switching, and
> counter reading of core PMUs on Kunpeng SoC. It facilitates fine-grained
> and multi-PMU-event CPU profiling, in which scenario the current 'perf'
> scheme may lose events or drop sampling frequency. With PMCU, users can
> reliably obtain the data of up to 240 PMU events with the sample interval
> of events down to 1ms, while the software overhead of accessing PMUs, as
> well as its impact on target workloads, is reduced.
>
> This patchset contains the documentation, driver, and user perf tool
> support to enable using PMCU with the 'perf_event' framework.
>
> Here are two key questions requested for comments:
>
> - How do we make it compatible with arm_pmu drivers?
>
>    Hardware-wise, PMCU uses the existing core PMUs, so PMUs can be accessed
>    from CPU and PMCU simultaneously. The current hardware can't guarantee
>    mutual exclusive accesses. Hence, scheduling arm_pmu and PMCU events at
>    the same time may mess up the operation of PMUs, delivering incorrect
>    data for both events, e.g. unexpected events or sample periods.
>    Software-wise, we probably need to prevent the two types of events from
>    running at the same time, but currently there isn't a clear solution.
>
> - Currently we reply on a sysfs file for users to input event numbers. Is
>    there a better way to pass many events?
>
>    The perf framework only allows three 64-bit config fields for custom PMU
>    configs. Obviously, this can't satisfy our need for passing many events
>    at a time. As an event number is 16-bit wide, the config fields can only
>    take up to 12 events at a time, or up to 192 events even if we do a
>    bitmap of events (and there are more than 192 available event numbers).
>    Hence, the current design takes an array of event numbers from a sysfs
>    file before starting profiling. However, this may go against the common
>    way to schedule perf events through perf commands.
>
> Jie Zhan (4):
>    docs: perf: Add documentation for HiSilicon PMCU
>    drivers/perf: hisi: Add driver support for HiSilicon PMCU
>    perf tool: Add HiSilicon PMCU data recording support
>    perf tool: Add HiSilicon PMCU data decoding support
>
>   Documentation/admin-guide/perf/hisi-pmcu.rst |  183 +++
>   Documentation/admin-guide/perf/index.rst     |    1 +
>   drivers/perf/hisilicon/Kconfig               |   15 +
>   drivers/perf/hisilicon/Makefile              |    1 +
>   drivers/perf/hisilicon/hisi_pmcu.c           | 1096 ++++++++++++++++++
>   tools/perf/arch/arm/util/auxtrace.c          |   61 +
>   tools/perf/arch/arm64/util/Build             |    2 +-
>   tools/perf/arch/arm64/util/hisi-pmcu.c       |  145 +++
>   tools/perf/util/Build                        |    1 +
>   tools/perf/util/auxtrace.c                   |    4 +
>   tools/perf/util/auxtrace.h                   |    1 +
>   tools/perf/util/hisi-pmcu.c                  |  305 +++++
>   tools/perf/util/hisi-pmcu.h                  |   19 +
>   13 files changed, 1833 insertions(+), 1 deletion(-)
>   create mode 100644 Documentation/admin-guide/perf/hisi-pmcu.rst
>   create mode 100644 drivers/perf/hisilicon/hisi_pmcu.c
>   create mode 100644 tools/perf/arch/arm64/util/hisi-pmcu.c
>   create mode 100644 tools/perf/util/hisi-pmcu.c
>   create mode 100644 tools/perf/util/hisi-pmcu.h
>
>
> base-commit: 830b3c68c1fb1e9176028d02ef86f3cf76aa2476