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Message-ID: <20250407154912.3c6c6246@gandalf.local.home>
Date: Mon, 7 Apr 2025 15:49:12 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
<linux-trace-kernel@...r.kernel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com>, Tom Zanussi <zanussi@...nel.org>
Subject: [PATCH] tracing: Add common_comm to histograms
From: Steven Rostedt <rostedt@...dmis.org>
If one wants to trace the name of the task that wakes up a process and
pass that to the synthetic events, there's nothing currently that lets the
synthetic events do that. Add a "common_comm" to the histogram logic that
allows histograms save the current->comm as a variable that can be passed
through and added to a synthetic event:
# cd /sys/kernel/tracing
# echo 's:wake_lat char[] waker; char[] wakee; u64 delta;' >> dynamic_events
# echo 'hist:keys=pid:comm=common_comm:ts=common_timestamp.usecs if !(common_flags & 0x18)' > events/sched/sched_waking/trigger
# echo 'hist:keys=next_pid:wake_comm=$comm:delta=common_timestamp.usecs-$ts:onmatch(sched.sched_waking).trace(wake_lat,$wake_comm,next_comm,$delta)' > events/sched/sched_switch/trigger
The above will create a synthetic trace event that will save both the name
of the waker and the wakee but only if the wakeup did not happen in a hard
or soft interrupt context.
The "common_comm" is used to save the task->comm at the time of the
initial event and is passed via the "comm" variable to the second event,
and that is saved as the "waker" field in the "wake_lat" synthetic event.
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
kernel/trace/trace_events_hist.c | 51 ++++++++++++++++++++++++++------
1 file changed, 42 insertions(+), 9 deletions(-)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index e85bc59c0421..58c9535f61df 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -114,6 +114,7 @@ enum hist_field_fn {
HIST_FIELD_FN_BUCKET,
HIST_FIELD_FN_TIMESTAMP,
HIST_FIELD_FN_CPU,
+ HIST_FIELD_FN_COMM,
HIST_FIELD_FN_STRING,
HIST_FIELD_FN_DYNSTRING,
HIST_FIELD_FN_RELDYNSTRING,
@@ -506,6 +507,7 @@ enum hist_field_flags {
HIST_FIELD_FL_CONST = 1 << 18,
HIST_FIELD_FL_PERCENT = 1 << 19,
HIST_FIELD_FL_GRAPH = 1 << 20,
+ HIST_FIELD_FL_COMM = 1 << 21,
};
struct var_defs {
@@ -885,6 +887,15 @@ static u64 hist_field_cpu(struct hist_field *hist_field,
return cpu;
}
+static u64 hist_field_comm(struct hist_field *hist_field,
+ struct tracing_map_elt *elt,
+ struct trace_buffer *buffer,
+ struct ring_buffer_event *rbe,
+ void *event)
+{
+ return (u64)(unsigned long)current->comm;
+}
+
/**
* check_field_for_var_ref - Check if a VAR_REF field references a variable
* @hist_field: The VAR_REF field to check
@@ -1338,6 +1349,8 @@ static const char *hist_field_name(struct hist_field *field,
field_name = hist_field_name(field->operands[0], ++level);
else if (field->flags & HIST_FIELD_FL_CPU)
field_name = "common_cpu";
+ else if (field->flags & HIST_FIELD_FL_COMM)
+ field_name = "common_comm";
else if (field->flags & HIST_FIELD_FL_EXPR ||
field->flags & HIST_FIELD_FL_VAR_REF) {
if (field->system) {
@@ -2015,6 +2028,13 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
goto out;
}
+ if (flags & HIST_FIELD_FL_COMM) {
+ hist_field->fn_num = HIST_FIELD_FN_COMM;
+ hist_field->size = MAX_FILTER_STR_VAL;
+ hist_field->type = "char[]";
+ goto out;
+ }
+
if (WARN_ON_ONCE(!field))
goto out;
@@ -2359,9 +2379,11 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
hist_data->attrs->ts_in_usecs = true;
} else if (strcmp(field_name, "common_stacktrace") == 0) {
*flags |= HIST_FIELD_FL_STACKTRACE;
- } else if (strcmp(field_name, "common_cpu") == 0)
+ } else if (strcmp(field_name, "common_cpu") == 0) {
*flags |= HIST_FIELD_FL_CPU;
- else if (strcmp(field_name, "hitcount") == 0)
+ } else if (strcmp(field_name, "common_comm") == 0) {
+ *flags |= HIST_FIELD_FL_COMM | HIST_FIELD_FL_STRING;
+ } else if (strcmp(field_name, "hitcount") == 0)
*flags |= HIST_FIELD_FL_HITCOUNT;
else {
field = trace_find_event_field(file->event_call, field_name);
@@ -2377,6 +2399,8 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
*flags |= HIST_FIELD_FL_CPU;
} else if (field && field->filter_type == FILTER_STACKTRACE) {
*flags |= HIST_FIELD_FL_STACKTRACE;
+ } else if (field && field->filter_type == FILTER_COMM) {
+ *flags |= HIST_FIELD_FL_COMM | HIST_FIELD_FL_STRING;
} else {
hist_err(tr, HIST_ERR_FIELD_NOT_FOUND,
errpos(field_name));
@@ -4327,6 +4351,8 @@ static u64 hist_fn_call(struct hist_field *hist_field,
return hist_field_timestamp(hist_field, elt, buffer, rbe, event);
case HIST_FIELD_FN_CPU:
return hist_field_cpu(hist_field, elt, buffer, rbe, event);
+ case HIST_FIELD_FN_COMM:
+ return hist_field_comm(hist_field, elt, buffer, rbe, event);
case HIST_FIELD_FN_STRING:
return hist_field_string(hist_field, elt, buffer, rbe, event);
case HIST_FIELD_FN_DYNSTRING:
@@ -5212,14 +5238,19 @@ static inline void add_to_key(char *compound_key, void *key,
size_t size = key_field->size;
if (key_field->flags & HIST_FIELD_FL_STRING) {
- struct ftrace_event_field *field;
- field = key_field->field;
- if (field->filter_type == FILTER_DYN_STRING ||
- field->filter_type == FILTER_RDYN_STRING)
- size = *(u32 *)(rec + field->offset) >> 16;
- else if (field->filter_type == FILTER_STATIC_STRING)
- size = field->size;
+ if (key_field->flags & HIST_FIELD_FL_COMM) {
+ size = strlen((char *)key);
+ } else {
+ struct ftrace_event_field *field;
+
+ field = key_field->field;
+ if (field->filter_type == FILTER_DYN_STRING ||
+ field->filter_type == FILTER_RDYN_STRING)
+ size = *(u32 *)(rec + field->offset) >> 16;
+ else if (field->filter_type == FILTER_STATIC_STRING)
+ size = field->size;
+ }
/* ensure NULL-termination */
if (size > key_field->size - 1)
@@ -6097,6 +6128,8 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
if (hist_field->flags & HIST_FIELD_FL_CPU)
seq_puts(m, "common_cpu");
+ if (hist_field->flags & HIST_FIELD_FL_COMM)
+ seq_puts(m, "common_comm");
else if (hist_field->flags & HIST_FIELD_FL_CONST)
seq_printf(m, "%llu", hist_field->constant);
else if (field_name) {
--
2.47.2
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