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authorPawel Moll <pawel.moll@arm.com>2014-07-22 18:32:59 +0100
committerArnd Bergmann <arnd@arndb.de>2014-07-23 22:14:43 +0200
commita33b0daab73a0e08cc04459dd44b0121a8e8f81b (patch)
treee7c432add19822871a057313264825c85e9cdf80 /Documentation/arm
parent779ae55bd8ee63f2ba35a0ec15f033e512e706ee (diff)
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bus: ARM CCN PMU driver
Driver providing perf backend for ARM Cache Coherent Network interconnect. Supports counting all hardware events and crosspoint watchpoints. Currently works with CCN-504 only, although there should be no changes required for CCN-508 (just impossible to test it now). Signed-off-by: Pawel Moll <pawel.moll@arm.com> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
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+ARM Cache Coherent Network
+==========================
+
+CCN-504 is a ring-bus interconnect consisting of 11 crosspoints
+(XPs), with each crosspoint supporting up to two device ports,
+so nodes (devices) 0 and 1 are connected to crosspoint 0,
+nodes 2 and 3 to crosspoint 1 etc.
+
+PMU (perf) driver
+-----------------
+
+The CCN driver registers a perf PMU driver, which provides
+description of available events and configuration options
+in sysfs, see /sys/bus/event_source/devices/ccn*.
+
+The "format" directory describes format of the config, config1
+and config2 fields of the perf_event_attr structure. The "events"
+directory provides configuration templates for all documented
+events, that can be used with perf tool. For example "xp_valid_flit"
+is an equivalent of "type=0x8,event=0x4". Other parameters must be
+explicitly specified. For events originating from device, "node"
+defines its index. All crosspoint events require "xp" (index),
+"port" (device port number) and "vc" (virtual channel ID) and
+"dir" (direction). Watchpoints (special "event" value 0xfe) also
+require comparator values ("cmp_l" and "cmp_h") and "mask", being
+index of the comparator mask.
+
+Masks are defined separately from the event description
+(due to limited number of the config values) in the "cmp_mask"
+directory, with first 8 configurable by user and additional
+4 hardcoded for the most frequent use cases.
+
+Cycle counter is described by a "type" value 0xff and does
+not require any other settings.
+
+Example of perf tool use:
+
+/ # perf list | grep ccn
+ ccn/cycles/ [Kernel PMU event]
+<...>
+ ccn/xp_valid_flit/ [Kernel PMU event]
+<...>
+
+/ # perf stat -C 0 -e ccn/cycles/,ccn/xp_valid_flit,xp=1,port=0,vc=1,dir=1/ \
+ sleep 1
+
+The driver does not support sampling, therefore "perf record" will
+not work. Also notice that only single cpu is being selected
+("-C 0") - this is because perf framework does not support
+"non-CPU related" counters (yet?) so system-wide session ("-a")
+would try (and in most cases fail) to set up the same event
+per each CPU.
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