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    SubjectRe: [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you can
    On Mon, 16 Apr 2018 21:07:47 -0700
    Joel Fernandes <joelaf@google.com> 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 <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
    >


    --
    Masami Hiramatsu <mhiramat@kernel.org>

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