Re: [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you can
From: Joel Fernandes
Date: Mon Apr 30 2018 - 21:18:48 EST
On Wed, Apr 18, 2018 at 2:02 AM Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> On Mon, 16 Apr 2018 21:07:47 -0700
> Joel Fernandes <joelaf@xxxxxxxxxx> 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
> int disabled = irqs_disabled();
> if (!raw_irqs_disabled_flags(flags) && disabled)
> if (raw_irqs_disabled_flags(flags) && !disabled)
With changes to the tracepoint implementation which uses srcu instead of
rcu, I'm not able to see a performance improvement with the above patch.
For this reason, I will drop this patch from next series. thanks,