[PATCH v4] tracing: Record trace_clock and recover when reboot
From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Date: 2025-05-14 07:04:21
Also in:
lkml
Subsystem:
the rest, tracing · Maintainers:
Linus Torvalds, Steven Rostedt, Masami Hiramatsu
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Record trace_clock information in the trace_scratch area and recover
the trace_clock when boot, so that reader can docode the timestamp
correctly.
Note that since most trace_clocks records the timestamp in nano-
seconds, this is not a bug. But some trace_clock, like counter and
tsc will record the counter value. Only for those trace_clock user
needs this information.
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v4:
- Use unsigned int instead of int for clock_id.
- Check trace_scratch::clock_id is sane.
Changes in v3:
- Save clock_id instead of its name.
Changes in v2:
- instead of exposing it via last_boot_info, set the current
trace_clock as the same clock we used in the last boot.
---
kernel/trace/trace.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index cf51c30b137f..2c1764ed87b0 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c@@ -6066,6 +6066,7 @@ struct trace_mod_entry { }; struct trace_scratch { + unsigned int clock_id; unsigned long text_addr; unsigned long nr_entries; struct trace_mod_entry entries[];
@@ -6181,6 +6182,7 @@ static void update_last_data(struct trace_array *tr) if (tr->scratch) { struct trace_scratch *tscratch = tr->scratch; + tscratch->clock_id = tr->clock_id; memset(tscratch->entries, 0, flex_array_size(tscratch, entries, tscratch->nr_entries)); tscratch->nr_entries = 0;
@@ -7403,6 +7405,12 @@ int tracing_set_clock(struct trace_array *tr, const char *clockstr) tracing_reset_online_cpus(&tr->max_buffer); #endif + if (tr->scratch && !(tr->flags & TRACE_ARRAY_FL_LAST_BOOT)) { + struct trace_scratch *tscratch = tr->scratch; + + tscratch->clock_id = i; + } + mutex_unlock(&trace_types_lock); return 0;
@@ -9628,6 +9636,15 @@ static void setup_trace_scratch(struct trace_array *tr, /* Scan modules to make text delta for modules. */ module_for_each_mod(make_mod_delta, tr); + + /* Set trace_clock as the same of the previous boot. */ + if (tscratch->clock_id != tr->clock_id) { + if (tscratch->clock_id >= ARRAY_SIZE(trace_clocks) || + tracing_set_clock(tr, trace_clocks[tscratch->clock_id].name) < 0) { + pr_info("the previous trace_clock info is not valid."); + goto reset; + } + } return; reset: /* Invalid trace modules */