linux-kernel - [PATCH 1/2] trace/preemptirq: reduce overhead of irq

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250626142017.26372-2-wander@redhat.com>
Date: Thu, 26 Jun 2025 11:20:09 -0300
From: Wander Lairson Costa <wander@...hat.com>
To: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Boqun Feng <boqun.feng@...il.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	Wander Lairson Costa <wander@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org (open list),
	linux-trace-kernel@...r.kernel.org (open list:TRACING)
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
	Clark Williams <williams@...hat.com>,
	Gabriele Monaco <gmonaco@...hat.com>
Subject: [PATCH 1/2] trace/preemptirq: reduce overhead of irq_enable/disable tracepoints

The irqsoff tracer is rarely enabled in production systems due to the
non-negligible overhead it introduces—even when unused. This is caused
by how trace_hardirqs_on/off() are always invoked in
local_irq_enable/disable(), evaluate the tracepoint static key.

This patch reduces the overhead in the common case where the tracepoint
is disabled by performing the static key check earlier, avoiding the
call to trace_hardirqs_on/off() entirely.

This makes the impact of disabled preemptirq IRQ tracing negligible in
performance-sensitive environments.

Signed-off-by: Wander Lairson Costa <wander@...hat.com>
Suggested-by: Steven Rostedt <rostedt@...dmis.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Clark Williams <williams@...hat.com>
Cc: Gabriele Monaco <gmonaco@...hat.com>
Cc: Juri Lelli <juri.lelli@...hat.com>
---
 include/linux/irqflags.h        | 25 +++++++++++++++++--------
 kernel/trace/trace_preemptirq.c |  3 +++
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 57b074e0cfbb..54f931db7e3b 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -17,6 +17,7 @@
 #include <linux/cleanup.h>
 #include <asm/irqflags.h>
 #include <asm/percpu.h>
+#include <linux/tracepoint-defs.h>
 
 struct task_struct;
 
@@ -197,9 +198,13 @@ extern void warn_bogus_irq_restore(void);
  */
 #ifdef CONFIG_TRACE_IRQFLAGS
 
+DECLARE_TRACEPOINT(irq_enable);
+DECLARE_TRACEPOINT(irq_disable);
+
 #define local_irq_enable()				\
 	do {						\
-		trace_hardirqs_on();			\
+		if (tracepoint_enabled(irq_enable))	\
+			trace_hardirqs_on();		\
 		raw_local_irq_enable();			\
 	} while (0)
 
@@ -207,28 +212,32 @@ extern void warn_bogus_irq_restore(void);
 	do {						\
 		bool was_disabled = raw_irqs_disabled();\
 		raw_local_irq_disable();		\
-		if (!was_disabled)			\
+		if (tracepoint_enabled(irq_disable) &&	\
+		    !was_disabled)			\
 			trace_hardirqs_off();		\
 	} while (0)
 
 #define local_irq_save(flags)				\
 	do {						\
 		raw_local_irq_save(flags);		\
-		if (!raw_irqs_disabled_flags(flags))	\
+		if (tracepoint_enabled(irq_disable) &&	\
+		    !raw_irqs_disabled_flags(flags))	\
 			trace_hardirqs_off();		\
 	} while (0)
 
 #define local_irq_restore(flags)			\
 	do {						\
-		if (!raw_irqs_disabled_flags(flags))	\
+		if (tracepoint_enabled(irq_enable) &&	\
+		    !raw_irqs_disabled_flags(flags))	\
 			trace_hardirqs_on();		\
 		raw_local_irq_restore(flags);		\
 	} while (0)
 
-#define safe_halt()				\
-	do {					\
-		trace_hardirqs_on();		\
-		raw_safe_halt();		\
+#define safe_halt()					\
+	do {						\
+		if (tracepoint_enabled(irq_enable))	\
+			trace_hardirqs_on();		\
+		raw_safe_halt();			\
 	} while (0)
 
 
diff --git a/kernel/trace/trace_preemptirq.c b/kernel/trace/trace_preemptirq.c
index 0c42b15c3800..90ee65db4516 100644
--- a/kernel/trace/trace_preemptirq.c
+++ b/kernel/trace/trace_preemptirq.c
@@ -111,6 +111,9 @@ void trace_hardirqs_off(void)
 }
 EXPORT_SYMBOL(trace_hardirqs_off);
 NOKPROBE_SYMBOL(trace_hardirqs_off);
+
+EXPORT_TRACEPOINT_SYMBOL(irq_disable);
+EXPORT_TRACEPOINT_SYMBOL(irq_enable);
 #endif /* CONFIG_TRACE_IRQFLAGS */
 
 #ifdef CONFIG_TRACE_PREEMPT_TOGGLE
-- 
2.50.0