* [PATCH 1/2] tracing: Fix fully-qualified variable reference printing in histograms
2026-04-13 22:35 [PATCH 0/2] tracing: fully-qualified var-ref testcase Tom Zanussi
@ 2026-04-13 22:35 ` Tom Zanussi
2026-04-13 22:35 ` [PATCH 2/2] selftests/ftrace: Add test case for fully-qualified variable references Tom Zanussi
1 sibling, 0 replies; 3+ messages in thread
From: Tom Zanussi @ 2026-04-13 22:35 UTC (permalink / raw)
To: rostedt
Cc: pengpeng, mhiramat, mathieu.desnoyers, linux-kernel,
linux-trace-kernel
The syntax for fully-qualified variable references in histograms is
subsys.event.$var, which is parsed correctly, but not displayed
correctly when printing a histogram spec. The current code puts the $
reference at the beginning of the fully-qualified variable name
i.e. $subsys.event.var, which is incorrect.
Before:
trigger info: hist:keys=next_comm:vals=hitcount:wakeup_lat=common_timestamp.usecs-$sched.sched_wakeup.ts0: ...
After:
trigger info: hist:keys=next_comm:vals=hitcount:wakeup_lat=common_timestamp.usecs-sched.sched_wakeup.$ts0: ...
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
---
kernel/trace/trace_events_hist.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index b2b675c7d663..0dbbf6cca9bc 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1361,9 +1361,12 @@ static const char *hist_field_name(struct hist_field *field,
field->flags & HIST_FIELD_FL_VAR_REF) {
if (field->system) {
static char full_name[MAX_FILTER_STR_VAL];
+ static char *fmt;
int len;
- len = snprintf(full_name, sizeof(full_name), "%s.%s.%s",
+ fmt = field->flags & HIST_FIELD_FL_VAR_REF ? "%s.%s.$%s" : "%s.%s.%s";
+
+ len = snprintf(full_name, sizeof(full_name), fmt,
field->system, field->event_name,
field->name);
if (len >= sizeof(full_name))
@@ -1742,9 +1745,10 @@ static const char *get_hist_field_flags(struct hist_field *hist_field)
static void expr_field_str(struct hist_field *field, char *expr)
{
- if (field->flags & HIST_FIELD_FL_VAR_REF)
- strcat(expr, "$");
- else if (field->flags & HIST_FIELD_FL_CONST) {
+ if (field->flags & HIST_FIELD_FL_VAR_REF) {
+ if (!field->system)
+ strcat(expr, "$");
+ } else if (field->flags & HIST_FIELD_FL_CONST) {
char str[HIST_CONST_DIGITS_MAX];
snprintf(str, HIST_CONST_DIGITS_MAX, "%llu", field->constant);
@@ -6156,7 +6160,8 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
else if (field_name) {
if (hist_field->flags & HIST_FIELD_FL_VAR_REF ||
hist_field->flags & HIST_FIELD_FL_ALIAS)
- seq_putc(m, '$');
+ if (!hist_field->system)
+ seq_putc(m, '$');
seq_printf(m, "%s", field_name);
} else if (hist_field->flags & HIST_FIELD_FL_TIMESTAMP)
seq_puts(m, "common_timestamp");
--
2.43.0
^ permalink raw reply related [flat|nested] 3+ messages in thread* [PATCH 2/2] selftests/ftrace: Add test case for fully-qualified variable references
2026-04-13 22:35 [PATCH 0/2] tracing: fully-qualified var-ref testcase Tom Zanussi
2026-04-13 22:35 ` [PATCH 1/2] tracing: Fix fully-qualified variable reference printing in histograms Tom Zanussi
@ 2026-04-13 22:35 ` Tom Zanussi
1 sibling, 0 replies; 3+ messages in thread
From: Tom Zanussi @ 2026-04-13 22:35 UTC (permalink / raw)
To: rostedt
Cc: pengpeng, mhiramat, mathieu.desnoyers, linux-kernel,
linux-trace-kernel
This test adds a variable (ts0) to two events (sched_waking and
sched_wakeup) and uses a fully-qualified variable reference to
expicitly choose a particular one (sched_wakeup.$ts0) when calculating
the wakeup latency.
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
---
.../trigger-fully-qualified-var-ref.tc | 34 +++++++++++++++++++
1 file changed, 34 insertions(+)
create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-fully-qualified-var-ref.tc
diff --git a/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-fully-qualified-var-ref.tc b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-fully-qualified-var-ref.tc
new file mode 100644
index 000000000000..8d12cdd06f1d
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-fully-qualified-var-ref.tc
@@ -0,0 +1,34 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: event trigger - test fully-qualified variable reference support
+# requires: set_event synthetic_events events/sched/sched_process_fork/hist ping:program
+
+fail() { #msg
+ echo $1
+ exit_fail
+}
+
+echo "Test fully-qualified variable reference support"
+
+echo 'wakeup_latency u64 lat; pid_t pid; int prio; char comm[16]' > synthetic_events
+echo 'hist:keys=comm:ts0=common_timestamp.usecs if comm=="ping"' > events/sched/sched_waking/trigger
+echo 'hist:keys=comm:ts0=common_timestamp.usecs if comm=="ping"' > events/sched/sched_wakeup/trigger
+echo 'hist:keys=next_comm:wakeup_lat=common_timestamp.usecs-sched.sched_wakeup.$ts0:onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,next_pid,sched.sched_waking.prio,next_comm) if next_comm=="ping"' > events/sched/sched_switch/trigger
+echo 'hist:keys=pid,prio,comm:vals=lat:sort=pid,prio' > events/synthetic/wakeup_latency/trigger
+
+ping $LOCALHOST -c 3
+if ! grep -q "ping" events/synthetic/wakeup_latency/hist; then
+ fail "Failed to create inter-event histogram"
+fi
+
+if ! grep -q "synthetic_prio=prio" events/sched/sched_waking/hist; then
+ fail "Failed to create histogram with fully-qualified variable reference"
+fi
+
+echo '!hist:keys=next_comm:wakeup_lat=common_timestamp.usecs-sched.sched_wakeup.$ts0:onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,next_pid,sched.sched_waking.prio,next_comm) if next_comm=="ping"' >> events/sched/sched_switch/trigger
+
+if grep -q "synthetic_prio=prio" events/sched/sched_waking/hist; then
+ fail "Failed to remove histogram with fully-qualified variable reference"
+fi
+
+exit 0
--
2.43.0
^ permalink raw reply related [flat|nested] 3+ messages in thread