| Pawel Moll | a33b0da | 2014-07-22 18:32:59 +0100 | [diff] [blame] | 1 | ARM Cache Coherent Network |
| 2 | ========================== |
| 3 | |
| 4 | CCN-504 is a ring-bus interconnect consisting of 11 crosspoints |
| 5 | (XPs), with each crosspoint supporting up to two device ports, |
| 6 | so nodes (devices) 0 and 1 are connected to crosspoint 0, |
| 7 | nodes 2 and 3 to crosspoint 1 etc. |
| 8 | |
| 9 | PMU (perf) driver |
| 10 | ----------------- |
| 11 | |
| 12 | The CCN driver registers a perf PMU driver, which provides |
| 13 | description of available events and configuration options |
| 14 | in sysfs, see /sys/bus/event_source/devices/ccn*. |
| 15 | |
| 16 | The "format" directory describes format of the config, config1 |
| 17 | and config2 fields of the perf_event_attr structure. The "events" |
| 18 | directory provides configuration templates for all documented |
| 19 | events, that can be used with perf tool. For example "xp_valid_flit" |
| 20 | is an equivalent of "type=0x8,event=0x4". Other parameters must be |
| 21 | explicitly specified. For events originating from device, "node" |
| 22 | defines its index. All crosspoint events require "xp" (index), |
| 23 | "port" (device port number) and "vc" (virtual channel ID) and |
| 24 | "dir" (direction). Watchpoints (special "event" value 0xfe) also |
| 25 | require comparator values ("cmp_l" and "cmp_h") and "mask", being |
| 26 | index of the comparator mask. |
| 27 | |
| 28 | Masks are defined separately from the event description |
| 29 | (due to limited number of the config values) in the "cmp_mask" |
| 30 | directory, with first 8 configurable by user and additional |
| 31 | 4 hardcoded for the most frequent use cases. |
| 32 | |
| 33 | Cycle counter is described by a "type" value 0xff and does |
| 34 | not require any other settings. |
| 35 | |
| 36 | Example of perf tool use: |
| 37 | |
| 38 | / # perf list | grep ccn |
| 39 | ccn/cycles/ [Kernel PMU event] |
| 40 | <...> |
| 41 | ccn/xp_valid_flit/ [Kernel PMU event] |
| 42 | <...> |
| 43 | |
| 44 | / # perf stat -C 0 -e ccn/cycles/,ccn/xp_valid_flit,xp=1,port=0,vc=1,dir=1/ \ |
| 45 | sleep 1 |
| 46 | |
| 47 | The driver does not support sampling, therefore "perf record" will |
| 48 | not work. Also notice that only single cpu is being selected |
| 49 | ("-C 0") - this is because perf framework does not support |
| 50 | "non-CPU related" counters (yet?) so system-wide session ("-a") |
| 51 | would try (and in most cases fail) to set up the same event |
| 52 | per each CPU. |