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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.
- Crosspoint PMU events require "xp" (index), "bus" (bus number)
- and "vc" (virtual channel ID).
- Crosspoint watchpoint-based events (special "event" value 0xfe)
- require "xp" and "vc" as as above plus "port" (device port index),
- "dir" (transmit/receive direction), 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.
- The driver also provides a "cpumask" sysfs attribute, which contains
- a single CPU ID, of the processor which will be used to handle all
- the CCN PMU events. It is recommended that the user space tools
- request the events on this processor (if not, the perf_event->cpu value
- will be overwritten anyway). In case of this processor being offlined,
- the events are migrated to another one and the attribute is updated.
- Example of perf tool use:
- / # perf list | grep ccn
- ccn/cycles/ [Kernel PMU event]
- <...>
- ccn/xp_valid_flit,xp=?,port=?,vc=?,dir=?/ [Kernel PMU event]
- <...>
- / # perf stat -a -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. Per-task (without "-a") perf sessions are not supported.
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