[PATCH v3 1/5] Documentation: perf: stm32: ddrperfm support

From: Gerald BAEZA
Date: Tue Aug 27 2019 - 11:09:02 EST

The DDRPERFM is the DDR Performance Monitor embedded in STM32MP1 SOC.

This documentation introduces the DDRPERFM, the stm32-ddr-pmu driver
supporting it and how to use it with the perf tool.

Signed-off-by: Gerald Baeza <gerald.baeza@xxxxxx>
Documentation/perf/stm32-ddr-pmu.txt | 37 ++++++++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)
create mode 100644 Documentation/perf/stm32-ddr-pmu.txt

diff --git a/Documentation/perf/stm32-ddr-pmu.txt b/Documentation/perf/stm32-ddr-pmu.txt
new file mode 100644
index 0000000..557bf47
--- /dev/null
+++ b/Documentation/perf/stm32-ddr-pmu.txt
@@ -0,0 +1,37 @@
+STM32 DDR Performance Monitor (DDRPERFM)
+The DDRPERFM is the DDR Performance Monitor embedded in STM32MP1 SOC.
+See Documentation/arm/stm32/stm32mp157-overview.rst to get access to
+STM32MP157 reference manual RM0436 where DDRPERFM is described.
+The five following counters are supported by stm32-ddr-pmu driver:
+ cnt0: read operations counters (read_cnt)
+ cnt1: write operations counters (write_cnt)
+ cnt2: active state counters (activate_cnt)
+ cnt3: idle state counters (idle_cnt)
+ tcnt: time count, present for all sets (time_cnt)
+The stm32-ddr-pmu driver relies on the perf PMU framework to expose the
+counters via sysfs:
+ $ ls /sys/bus/event_source/devices/ddrperfm/events
+ activate_cnt idle_cnt read_cnt time_cnt write_cnt
+The perf PMU framework is usually invoked via the 'perf stat' tool.
+The DDRPERFM is a system monitor that cannot isolate the traffic coming from a
+given thread or CPU, that is why stm32-ddr-pmu driver rejects any 'perf stat'
+call that does not request a system-wide collection: the '-a, --all-cpus'
+option is mandatory!
+ $ perf stat -e ddrperfm/read_cnt/,ddrperfm/time_cnt/ -a sleep 20
+ Performance counter stats for 'system wide':
+ 342541560 ddrperfm/read_cnt/
+ 10660011400 ddrperfm/time_cnt/
+ 20.021068551 seconds time elapsed