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-rw-r--r--kernel/Documentation/arm/CCN.txt17
1 files changed, 10 insertions, 7 deletions
diff --git a/kernel/Documentation/arm/CCN.txt b/kernel/Documentation/arm/CCN.txt
index 0632b3aad..ffca443a1 100644
--- a/kernel/Documentation/arm/CCN.txt
+++ b/kernel/Documentation/arm/CCN.txt
@@ -33,20 +33,23 @@ directory, with first 8 configurable by user and additional
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/ [Kernel PMU event]
+ ccn/xp_valid_flit,xp=?,port=?,vc=?,dir=?/ [Kernel PMU event]
<...>
-/ # perf stat -C 0 -e ccn/cycles/,ccn/xp_valid_flit,xp=1,port=0,vc=1,dir=1/ \
+/ # 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. 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.
+not work. Per-task (without "-a") perf sessions are not supported.