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