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 <[email protected]> Suggested-by: Steven Rostedt <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Clark Williams <[email protected]> Cc: Gabriele Monaco <[email protected]> Cc: Juri Lelli <[email protected]> --- 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
