linux-kernel - Re: [PATCH v2 4/4] ftrace: Add an option for tracing console latencies

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Message-Id: <20190502183731.9571-1-viktor.rosendahl@gmail.com>
Date:   Thu,  2 May 2019 20:37:31 +0200
From:   Viktor Rosendahl <viktor.rosendahl@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Joel Fernandes <joel@...lfernandes.org>,
        Viktor Rosendahl <viktor.rosendahl@...il.com>
Subject: Re: [PATCH v2 4/4] ftrace: Add an option for tracing console latencies

> Instead of this being turned into a nop, don't have a kconfig option
> but instead have this call into the trace_irqsoff.c code, and depending
> on what the options are, it should stop it. Of course, this would need
> to be smart enough to pair it. Perhaps return the result of
> console_stop_critical_timings() and have that passed to
> console_start_critical_timings(), and only have start do something if
> stop did something. This way the option only needs to disable the stop
> part.

Something like this?

I have only compile tested it so far.

best regards,

Viktor
---
 include/linux/irqflags.h     | 17 +++++++++++++++++
 kernel/printk/printk.c       |  6 ++++--
 kernel/trace/trace.h         |  1 +
 kernel/trace/trace_irqsoff.c | 13 +++++++++++++
 4 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 21619c92c377..e4f7ebc67a53 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -68,9 +68,26 @@ do {						\
 	defined(CONFIG_PREEMPT_TRACER)
  extern void stop_critical_timings(void);
  extern void start_critical_timings(void);
+ extern bool console_tracing_disabled(void);
+
+#define console_stop_critical_timings(FLAG)		\
+	do {						\
+		FLAG = console_tracing_disabled();	\
+		if (FLAG)				\
+			stop_critical_timings();	\
+	} while(0)
+
+#define console_start_critical_timings(FLAG)		 \
+	do {						 \
+		if (FLAG)				 \
+			start_critical_timings();	 \
+	} while(0)
+
 #else
 # define stop_critical_timings() do { } while (0)
 # define start_critical_timings() do { } while (0)
+# define console_stop_critical_timings(FLAG) do { } while (0)
+# define console_start_critical_timings(FLAG) do { } while (0)
 #endif
 
 /*
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 02ca827b8fac..3a18b7208399 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2348,6 +2348,7 @@ void console_unlock(void)
 	static char ext_text[CONSOLE_EXT_LOG_MAX];
 	static char text[LOG_LINE_MAX + PREFIX_MAX];
 	unsigned long flags;
+	bool cflag;
 	bool do_cond_resched, retry;
 
 	if (console_suspended) {
@@ -2448,9 +2449,10 @@ void console_unlock(void)
 		 */
 		console_lock_spinning_enable();
 
-		stop_critical_timings();	/* don't trace print latency */
+		/* don't trace print latency if it's disabled */
+		console_stop_critical_timings(cflag);
 		call_console_drivers(ext_text, ext_len, text, len);
-		start_critical_timings();
+		console_start_critical_timings(cflag);
 
 		if (console_lock_spinning_disable_and_check()) {
 			printk_safe_exit_irqrestore(flags);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 59dc01ac52fd..3eed4756dba3 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1253,6 +1253,7 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
 		C(PRINTK_MSGONLY,	"printk-msg-only"),	\
 		C(CONTEXT_INFO,		"context-info"),   /* Print pid/cpu/time */ \
 		C(LATENCY_FMT,		"latency-format"),	\
+		C(CONSOLE_LATENCY,	"console-latency"),	\
 		C(RECORD_CMD,		"record-cmd"),		\
 		C(RECORD_TGID,		"record-tgid"),		\
 		C(OVERWRITE,		"overwrite"),		\
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 07a391e845de..659a82209c1e 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -490,6 +490,19 @@ void stop_critical_timings(void)
 EXPORT_SYMBOL_GPL(stop_critical_timings);
 NOKPROBE_SYMBOL(stop_critical_timings);
 
+bool console_tracing_disabled(void)
+{
+	struct trace_array *tr = irqsoff_trace;
+	int pc = preempt_count();
+
+	if (!preempt_trace(pc) && !irq_trace())
+		return false;
+
+	return !(tr->trace_flags & CONSOLE_LATENCY);
+}
+
+EXPORT_SYMBOL_GPL(console_tracing_disabled);
+
 #ifdef CONFIG_FUNCTION_TRACER
 static bool function_enabled;
 
-- 
2.17.1