Cavium ThunderX2 SoC Performance Monitoring Unit (PMU UNCORE)
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The ThunderX2 SoC PMU consists of independent, system-wide, per-socket
PMUs such as the Level 3 Cache (L3C) and DDR4 Memory Controller (DMC).

The DMC has 8 interleaved channels and the L3C has 16 interleaved tiles.
Events are counted for the default channel (i.e. channel 0) and prorated
to the total number of channels/tiles.

The DMC and L3C support up to 4 counters. Counters are independently
programmable and can be started and stopped individually. Each counter
can be set to a different event. Counters are 32-bit and do not support
an overflow interrupt; they are read every 2 seconds.

PMU UNCORE (perf) driver:

The thunderx2_pmu driver registers per-socket perf PMUs for the DMC and
L3C devices.  Each PMU can be used to count up to 4 events
simultaneously. The PMUs provide a description of their available events
and configuration options under sysfs, see
/sys/devices/uncore_<l3c_S/dmc_S/>; S is the socket id.

The driver does not support sampling, therefore "perf record" will not
work. Per-task perf sessions are also not supported.

Examples:

# perf stat -a -e uncore_dmc_0/cnt_cycles/ sleep 1

# perf stat -a -e \
uncore_dmc_0/cnt_cycles/,\
uncore_dmc_0/data_transfers/,\
uncore_dmc_0/read_txns/,\
uncore_dmc_0/write_txns/ sleep 1

# perf stat -a -e \
uncore_l3c_0/read_request/,\
uncore_l3c_0/read_hit/,\
uncore_l3c_0/inv_request/,\
uncore_l3c_0/inv_hit/ sleep 1
