Messages in this thread | | | Date | Thu, 19 Apr 2018 14:43:02 +0900 | From | Namhyung Kim <> | Subject | Re: [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you can |
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On Wed, Apr 18, 2018 at 06:02:50PM +0900, Masami Hiramatsu wrote: > 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,
I don't know how many it impacts on performance but maybe we can have an arch-specific config option something like below?
> 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 (disabled == raw_irqs_disabled_flags(flags)) { #ifndef CONFIG_ARCH_CAN_SKIP_NESTED_IRQ_RESTORE raw_local_irq_restore(flags); #endif return; }
> > 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();
Thanks, Namhyung
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