| 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. |