1APM X-Gene SoC Performance Monitoring Unit (PMU)
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3
4X-Gene SoC PMU consists of various independent system device PMUs such as
5L3 cache(s), I/O bridge(s), memory controller bridge(s) and memory
6controller(s). These PMU devices are loosely architected to follow the
7same model as the PMU for ARM cores. The PMUs share the same top level
8interrupt and status CSR region.
9
10PMU (perf) driver
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12
13The xgene-pmu driver registers several perf PMU drivers. Each of the perf
14driver provides description of its available events and configuration options
15in sysfs, see /sys/devices/<l3cX/iobX/mcbX/mcX>/.
16
17The "format" directory describes format of the config (event ID),
18config1 (agent ID) fields of the perf_event_attr structure. The "events"
19directory provides configuration templates for all supported event types that
20can be used with perf tool. For example, "l3c0/bank-fifo-full/" is an
21equivalent of "l3c0/config=0x0b/".
22
23Most of the SoC PMU has a specific list of agent ID used for monitoring
24performance of a specific datapath. For example, agents of a L3 cache can be
25a specific CPU or an I/O bridge. Each PMU has a set of 2 registers capable of
26masking the agents from which the request come from. If the bit with
27the bit number corresponding to the agent is set, the event is counted only if
28it is caused by a request from that agent. Each agent ID bit is inversely mapped
29to a corresponding bit in "config1" field. By default, the event will be
30counted for all agent requests (config1 = 0x0). For all the supported agents of
31each PMU, please refer to APM X-Gene User Manual.
32
33Each perf driver also provides a "cpumask" sysfs attribute, which contains a
34single CPU ID of the processor which will be used to handle all the PMU events.
35
36Example for perf tool use:
37
38 / # perf list | grep -e l3c -e iob -e mcb -e mc
39   l3c0/ackq-full/                                    [Kernel PMU event]
40 <...>
41   mcb1/mcb-csw-stall/                                [Kernel PMU event]
42
43 / # perf stat -a -e l3c0/read-miss/,mcb1/csw-write-request/ sleep 1
44
45 / # perf stat -a -e l3c0/read-miss,config1=0xfffffffffffffffe/ sleep 1
46
47The driver does not support sampling, therefore "perf record" will
48not work. Per-task (without "-a") perf sessions are not supported.
49