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authorSteven Rostedt (VMware) <rostedt@goodmis.org>2021-07-21 18:00:53 +0300
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2021-07-23 15:44:47 +0300
commit1e3bac71c5053c99d438771fc9fa5082ae5d90aa (patch)
treeaf8605ee3fd1d962b4fd5e400277d0ee4f937850 /Documentation
parent3b13911a2fd0dd0146c9777a254840c5466cf120 (diff)
downloadlinux-1e3bac71c5053c99d438771fc9fa5082ae5d90aa.tar.xz
tracing/histogram: Rename "cpu" to "common_cpu"
Currently the histogram logic allows the user to write "cpu" in as an event field, and it will record the CPU that the event happened on. The problem with this is that there's a lot of events that have "cpu" as a real field, and using "cpu" as the CPU it ran on, makes it impossible to run histograms on the "cpu" field of events. For example, if I want to have a histogram on the count of the workqueue_queue_work event on its cpu field, running: ># echo 'hist:keys=cpu' > events/workqueue/workqueue_queue_work/trigger Gives a misleading and wrong result. Change the command to "common_cpu" as no event should have "common_*" fields as that's a reserved name for fields used by all events. And this makes sense here as common_cpu would be a field used by all events. Now we can even do: ># echo 'hist:keys=common_cpu,cpu if cpu < 100' > events/workqueue/workqueue_queue_work/trigger ># cat events/workqueue/workqueue_queue_work/hist # event histogram # # trigger info: hist:keys=common_cpu,cpu:vals=hitcount:sort=hitcount:size=2048 if cpu < 100 [active] # { common_cpu: 0, cpu: 2 } hitcount: 1 { common_cpu: 0, cpu: 4 } hitcount: 1 { common_cpu: 7, cpu: 7 } hitcount: 1 { common_cpu: 0, cpu: 7 } hitcount: 1 { common_cpu: 0, cpu: 1 } hitcount: 1 { common_cpu: 0, cpu: 6 } hitcount: 2 { common_cpu: 0, cpu: 5 } hitcount: 2 { common_cpu: 1, cpu: 1 } hitcount: 4 { common_cpu: 6, cpu: 6 } hitcount: 4 { common_cpu: 5, cpu: 5 } hitcount: 14 { common_cpu: 4, cpu: 4 } hitcount: 26 { common_cpu: 0, cpu: 0 } hitcount: 39 { common_cpu: 2, cpu: 2 } hitcount: 184 Now for backward compatibility, I added a trick. If "cpu" is used, and the field is not found, it will fall back to "common_cpu" and work as it did before. This way, it will still work for old programs that use "cpu" to get the actual CPU, but if the event has a "cpu" as a field, it will get that event's "cpu" field, which is probably what it wants anyway. I updated the tracefs/README to include documentation about both the common_timestamp and the common_cpu. This way, if that text is present in the README, then an application can know that common_cpu is supported over just plain "cpu". Link: https://lkml.kernel.org/r/20210721110053.26b4f641@oasis.local.home Cc: Namhyung Kim <namhyung@kernel.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: stable@vger.kernel.org Fixes: 8b7622bf94a44 ("tracing: Add cpu field for hist triggers") Reviewed-by: Tom Zanussi <zanussi@kernel.org> Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/trace/histogram.rst2
1 files changed, 1 insertions, 1 deletions
diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst
index b71e09f745c3..f99be8062bc8 100644
--- a/Documentation/trace/histogram.rst
+++ b/Documentation/trace/histogram.rst
@@ -191,7 +191,7 @@ Documentation written by Tom Zanussi
with the event, in nanoseconds. May be
modified by .usecs to have timestamps
interpreted as microseconds.
- cpu int the cpu on which the event occurred.
+ common_cpu int the cpu on which the event occurred.
====================== ==== =======================================
Extended error information