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Subject[RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you can
Date
With TRACE_IRQFLAGS, we call trace_ API too many times. We don't need
to if local_irq_restore or local_irq_save didn't actually do anything.

This gives around a 4% improvement in performance when doing the
following command: "time find / > /dev/null"

Also its best to avoid these calls where possible, since in this series,
the RCU code in tracepoint.h seems to be call these quite a bit and I'd
like to keep this overhead low.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zilstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Glexiner <tglx@linutronix.de>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Fenguang Wu <fengguang.wu@intel.com>
Cc: Baohong Liu <baohong.liu@intel.com>
Cc: Vedang Patel <vedang.patel@intel.com>
Signed-off-by: Joel Fernandes <joelaf@google.com>
---
include/linux/irqflags.h | 21 +++++++++++----------
1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 9700f00bbc04..ea8df0ac57d3 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -104,19 +104,20 @@ do { \
#define local_irq_save(flags) \
do { \
raw_local_irq_save(flags); \
- trace_hardirqs_off(); \
+ if (!raw_irqs_disabled_flags(flags)) \
+ trace_hardirqs_off(); \
} while (0)


-#define local_irq_restore(flags) \
- do { \
- if (raw_irqs_disabled_flags(flags)) { \
- raw_local_irq_restore(flags); \
- trace_hardirqs_off(); \
- } else { \
- trace_hardirqs_on(); \
- raw_local_irq_restore(flags); \
- } \
+#define local_irq_restore(flags) \
+ do { \
+ if (raw_irqs_disabled_flags(flags) && !irqs_disabled()) { \
+ raw_local_irq_restore(flags); \
+ trace_hardirqs_off(); \
+ } else if (!raw_irqs_disabled_flags(flags) && irqs_disabled()) {\
+ trace_hardirqs_on(); \
+ raw_local_irq_restore(flags); \
+ } \
} while (0)

#define safe_halt() \
--
2.17.0.484.g0c8726318c-goog
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