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| APM X-Gene SoC Performance Monitoring Unit (PMU) | |
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| X-Gene SoC PMU consists of various independent system device PMUs such as | |
| L3 cache(s), I/O bridge(s), memory controller bridge(s) and memory | |
| controller(s). These PMU devices are loosely architected to follow the | |
| same model as the PMU for ARM cores. The PMUs share the same top level | |
| interrupt and status CSR region. | |
| PMU (perf) driver | |
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| The xgene-pmu driver registers several perf PMU drivers. Each of the perf | |
| driver provides description of its available events and configuration options | |
| in sysfs, see /sys/bus/event_source/devices/<l3cX/iobX/mcbX/mcX>/. | |
| The "format" directory describes format of the config (event ID), | |
| config1 (agent ID) fields of the perf_event_attr structure. The "events" | |
| directory provides configuration templates for all supported event types that | |
| can be used with perf tool. For example, "l3c0/bank-fifo-full/" is an | |
| equivalent of "l3c0/config=0x0b/". | |
| Most of the SoC PMU has a specific list of agent ID used for monitoring | |
| performance of a specific datapath. For example, agents of a L3 cache can be | |
| a specific CPU or an I/O bridge. Each PMU has a set of 2 registers capable of | |
| masking the agents from which the request come from. If the bit with | |
| the bit number corresponding to the agent is set, the event is counted only if | |
| it is caused by a request from that agent. Each agent ID bit is inversely mapped | |
| to a corresponding bit in "config1" field. By default, the event will be | |
| counted for all agent requests (config1 = 0x0). For all the supported agents of | |
| each PMU, please refer to APM X-Gene User Manual. | |
| Each perf driver also provides a "cpumask" sysfs attribute, which contains a | |
| single CPU ID of the processor which will be used to handle all the PMU events. | |
| Example for perf tool use:: | |
| / # perf list | grep -e l3c -e iob -e mcb -e mc | |
| l3c0/ackq-full/ [Kernel PMU event] | |
| <...> | |
| mcb1/mcb-csw-stall/ [Kernel PMU event] | |
| / # perf stat -a -e l3c0/read-miss/,mcb1/csw-write-request/ sleep 1 | |
| / # perf stat -a -e l3c0/read-miss,config1=0xfffffffffffffffe/ sleep 1 | |
| The driver does not support sampling, therefore "perf record" will | |
| not work. Per-task (without "-a") perf sessions are not supported. |