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ftrace: Add max field to function profiler stats

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The function profiler (trace_stat/function<cpu>) reports Hit, Time,
Avg and s^2 per function. Add a "max" field recording the maximum
single-call duration, which is valuable for real-time tuning and for
investigating occasional latency spikes.

Like Time/Avg, it honors the graph-time and sleep-time options, so it
reflects entry-to-return wall-clock latency.

Link: https://patch.msgid.link/20260924030108.2673654-1-yun.zhou@windriver.com
Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Yun Zhou 2026-09-24 11:01:08 +08:00 committed by Steven Rostedt
parent 188a5bfd87
commit 1054e526ce
1 changed files with 7 additions and 2 deletions
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9
kernel/trace/ftrace.c
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@ -428,6 +428,7 @@ struct ftrace_profile {
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
unsigned long long time;
unsigned long long time_squared;
unsigned long long time_max;
#endif
};
@ -530,9 +531,9 @@ static int function_stat_headers(struct seq_file *m)
{
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
seq_puts(m, " Function "
"Hit Time Avg s^2\n"
"Hit Time Avg s^2 max\n"
" -------- "
"--- ---- --- ---\n");
"--- ---- --- --- ---\n");
#else
seq_puts(m, " Function Hit\n"
" -------- ---\n");
@ -613,6 +614,8 @@ static int function_stat_show(struct seq_file *m, void *v)
trace_print_graph_duration(avg, &s);
trace_seq_puts(&s, " ");
trace_print_graph_duration(stddev, &s);
trace_seq_puts(&s, " ");
trace_print_graph_duration(rec->time_max, &s);
trace_print_seq(m, &s);
#endif
seq_putc(m, '\n');
@ -920,6 +923,8 @@ static void profile_graph_return(struct ftrace_graph_ret *trace,
if (rec) {
rec->time += calltime;
rec->time_squared += calltime * calltime;
if (calltime > rec->time_max)
rec->time_max = calltime;
}
}