Messages in this thread Patch in this message |  | | Date | Wed, 18 Apr 2018 18:02:50 +0900 | From | Masami Hiramatsu <> | Subject | Re: [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you can |
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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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