linux-kernel - Re: [PATCH v4 1/4] sched: Define sched_clock

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Message-ID: <CALOAHbC3h5QyOyCB99xyBwiw+NW7BEqcRDoRwfvTc3id1NM4=A@mail.gmail.com>
Date: Fri, 1 Nov 2024 19:55:00 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org, 
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, 
	mgorman@...e.de, vschneid@...hat.com, hannes@...xchg.org, surenb@...gle.com, 
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/4] sched: Define sched_clock_irqtime as static key

On Fri, Nov 1, 2024 at 6:06 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Nov 01, 2024 at 11:17:47AM +0800, Yafang Shao wrote:
> > Since CPU time accounting is a performance-critical path, let's define
> > sched_clock_irqtime as a static key to minimize potential overhead.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > ---
> >  kernel/sched/cputime.c | 16 +++++++---------
> >  kernel/sched/sched.h   |  1 +
> >  2 files changed, 8 insertions(+), 9 deletions(-)
> >
> > diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> > index 0bed0fa1acd9..d0b6ea737d04 100644
> > --- a/kernel/sched/cputime.c
> > +++ b/kernel/sched/cputime.c
> > @@ -7,6 +7,8 @@
> >   #include <asm/cputime.h>
> >  #endif
> >
> > +DEFINE_STATIC_KEY_FALSE(sched_clock_irqtime);
> > +
> >  #ifdef CONFIG_IRQ_TIME_ACCOUNTING
> >
> >  /*
> > @@ -22,16 +24,14 @@
> >   */
> >  DEFINE_PER_CPU(struct irqtime, cpu_irqtime);
> >
> > -static int sched_clock_irqtime;
> > -
> >  void enable_sched_clock_irqtime(void)
> >  {
> > -     sched_clock_irqtime = 1;
> > +     static_branch_enable(&sched_clock_irqtime);
> >  }
> >
> >  void disable_sched_clock_irqtime(void)
> >  {
> > -     sched_clock_irqtime = 0;
> > +     static_branch_disable(&sched_clock_irqtime);
> >  }
> >
> >  static void irqtime_account_delta(struct irqtime *irqtime, u64 delta,
> > @@ -57,7 +57,7 @@ void irqtime_account_irq(struct task_struct *curr, unsigned int offset)
> >       s64 delta;
> >       int cpu;
> >
> > -     if (!sched_clock_irqtime)
> > +     if (!static_branch_likely(&sched_clock_irqtime))
> >               return;
> >
> >       cpu = smp_processor_id();
> > @@ -90,8 +90,6 @@ static u64 irqtime_tick_accounted(u64 maxtime)
> >
> >  #else /* CONFIG_IRQ_TIME_ACCOUNTING */
> >
> > -#define sched_clock_irqtime  (0)
> > -
> >  static u64 irqtime_tick_accounted(u64 dummy)
> >  {
> >       return 0;
>
> This makes no sense... in the IRQ_TIME_ACCOUNTING=n case you shouldn't
> be using the static key.

will change it.

-- 
Regards
Yafang