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Documentation / arm / CCN.txt


Based on kernel version 4.16.1. Page generated on 2018-04-09 11:52 EST.

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.
22	
23	For events originating from device, "node" defines its index.
24	
25	Crosspoint PMU events require "xp" (index), "bus" (bus number)
26	and "vc" (virtual channel ID).
27	
28	Crosspoint watchpoint-based events (special "event" value 0xfe)
29	require "xp" and "vc" as as above plus "port" (device port index),
30	"dir" (transmit/receive direction), comparator values ("cmp_l"
31	and "cmp_h") and "mask", being index of the comparator mask.
32	Masks are defined separately from the event description
33	(due to limited number of the config values) in the "cmp_mask"
34	directory, with first 8 configurable by user and additional
35	4 hardcoded for the most frequent use cases.
36	
37	Cycle counter is described by a "type" value 0xff and does
38	not require any other settings.
39	
40	The driver also provides a "cpumask" sysfs attribute, which contains
41	a single CPU ID, of the processor which will be used to handle all
42	the CCN PMU events. It is recommended that the user space tools
43	request the events on this processor (if not, the perf_event->cpu value
44	will be overwritten anyway). In case of this processor being offlined,
45	the events are migrated to another one and the attribute is updated.
46	
47	Example of perf tool use:
48	
49	/ # perf list | grep ccn
50	  ccn/cycles/                                        [Kernel PMU event]
51	<...>
52	  ccn/xp_valid_flit,xp=?,port=?,vc=?,dir=?/          [Kernel PMU event]
53	<...>
54	
55	/ # perf stat -a -e ccn/cycles/,ccn/xp_valid_flit,xp=1,port=0,vc=1,dir=1/ \
56	                                                                       sleep 1
57	
58	The driver does not support sampling, therefore "perf record" will
59	not work. Per-task (without "-a") perf sessions are not supported.
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