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

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