From: "Steven Rostedt (VMware)" rostedt@goodmis.org
stable inclusion from linux-4.19.203 commit c0add455ae992b53b0d52cd4d8682528b4014c42
--------------------------------
commit 1e3bac71c5053c99d438771fc9fa5082ae5d90aa upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- Documentation/trace/histogram.rst | 2 +- kernel/trace/trace.c | 4 ++++ kernel/trace/trace_events_hist.c | 21 +++++++++++++++------ 3 files changed, 20 insertions(+), 7 deletions(-)
diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst index 5ac724baea7d9..c14dab13a47e8 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 diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 87fb10a886ce9..b2584a1eb37be 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4727,6 +4727,10 @@ static const char readme_msg[] = "\t [:pause][:continue][:clear]\n" "\t [:name=histname1]\n" "\t [if <filter>]\n\n" + "\t Note, special fields can be used as well:\n" + "\t common_timestamp - to record current timestamp\n" + "\t common_cpu - to record the CPU the event happened on\n" + "\n" "\t When a matching event is hit, an entry is added to a hash\n" "\t table using the key(s) and value(s) named, and the value of a\n" "\t sum called 'hitcount' is incremented. Keys and values\n" diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index c33e4cf345472..6d2a69652c391 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -1773,7 +1773,7 @@ static const char *hist_field_name(struct hist_field *field, field->flags & HIST_FIELD_FL_ALIAS) field_name = hist_field_name(field->operands[0], ++level); else if (field->flags & HIST_FIELD_FL_CPU) - field_name = "cpu"; + field_name = "common_cpu"; else if (field->flags & HIST_FIELD_FL_EXPR || field->flags & HIST_FIELD_FL_VAR_REF) { if (field->system) { @@ -2627,14 +2627,23 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file, hist_data->enable_timestamps = true; if (*flags & HIST_FIELD_FL_TIMESTAMP_USECS) hist_data->attrs->ts_in_usecs = true; - } else if (strcmp(field_name, "cpu") == 0) + } else if (strcmp(field_name, "common_cpu") == 0) *flags |= HIST_FIELD_FL_CPU; else { field = trace_find_event_field(file->event_call, field_name); if (!field || !field->size) { - hist_err("Couldn't find field: ", field_name); - field = ERR_PTR(-EINVAL); - goto out; + /* + * For backward compatibility, if field_name + * was "cpu", then we treat this the same as + * common_cpu. + */ + if (strcmp(field_name, "cpu") == 0) { + *flags |= HIST_FIELD_FL_CPU; + } else { + hist_err("Couldn't find field: ", field_name); + field = ERR_PTR(-EINVAL); + goto out; + } } } out: @@ -5052,7 +5061,7 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field) seq_printf(m, "%s=", hist_field->var.name);
if (hist_field->flags & HIST_FIELD_FL_CPU) - seq_puts(m, "cpu"); + seq_puts(m, "common_cpu"); else if (field_name) { if (hist_field->flags & HIST_FIELD_FL_VAR_REF || hist_field->flags & HIST_FIELD_FL_ALIAS)