On Mon, 16 Apr 2018 21:07:47 -0700
Joel Fernandes <[email protected]> wrote:
> 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.
Can we assume that the "flags" has only 1 bit irq-disable flag?
Since it skips calling raw_local_irq_restore(flags); too,
if there is any state in the flags on any arch, it may change the
result. In that case, we can do it as below (just skipping trace_hardirqs_*)
int disabled = irqs_disabled();
if (!raw_irqs_disabled_flags(flags) && disabled)
trace_hardirqs_on();
raw_local_irq_restore(flags);
if (raw_irqs_disabled_flags(flags) && !disabled)
trace_hardirqs_off();
Thank you,
>
> Cc: Steven Rostedt <[email protected]>
> Cc: Peter Zilstra <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Mathieu Desnoyers <[email protected]>
> Cc: Tom Zanussi <[email protected]>
> Cc: Namhyung Kim <[email protected]>
> Cc: Thomas Glexiner <[email protected]>
> Cc: Boqun Feng <[email protected]>
> Cc: Paul McKenney <[email protected]>
> Cc: Frederic Weisbecker <[email protected]>
> Cc: Randy Dunlap <[email protected]>
> Cc: Masami Hiramatsu <[email protected]>
> Cc: Fenguang Wu <[email protected]>
> Cc: Baohong Liu <[email protected]>
> Cc: Vedang Patel <[email protected]>
> Signed-off-by: Joel Fernandes <[email protected]>
> ---
> 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
>
--
Masami Hiramatsu <[email protected]>
