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
