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 | 41 ++++++++++++++++++++++++++++++++++++ 1 file changed, 41 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..d5b35b3 --- /dev/null +++ b/Documentation/perf/stm32-ddr-pmu.txt @@ -0,0 +1,41 @@ +STM32 DDR Performance Monitor (DDRPERFM) +======================================== + +The DDRPERFM is the DDR Performance Monitor embedded in STM32MP1 SOC. +See STM32MP157 reference manual RM0436 to get a description of this peripheral. + + +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! + +Example: + $ 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 + + +The driver also exposes a 'bandwidth' attribute that can be used to display +the read/write/total bandwidth achieved during the last 'perf stat' execution. + $ cat /sys/bus/event_source/devices/ddrperfm/bandwidth + Read = 403, Write = 239, Read & Write = 642 (MB/s) -- 2.7.4
