Re: [PATCH 2/2] intel_idle: Fix intel_idle() vs tracing

From: Peter Zijlstra <peterz@infradead.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>,
	Ingo Molnar <mingo@kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Will Deacon <will@kernel.org>,
	svens@linux.ibm.com,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] intel_idle: Fix intel_idle() vs tracing
Date: Mon, 23 Nov 2020 14:46:18 +0100	[thread overview]
Message-ID: <20201123134618.GL3021@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAJZ5v0hhSO36-m-otWp0vqWNNZFiDWPX-xxK-ninRr2d==QOWA@mail.gmail.com>

On Mon, Nov 23, 2020 at 11:26:39AM +0100, Rafael J. Wysocki wrote:
> On Fri, Nov 20, 2020 at 12:50 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > cpuidle->enter() callbacks should not call into tracing because RCU
> > has already been disabled. Instead of doing the broadcast thing
> > itself, simply advertise to the cpuidle core that those states stop
> > the timer.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> >  drivers/idle/intel_idle.c |   37 ++++++++++++++++++++-----------------
> >  1 file changed, 20 insertions(+), 17 deletions(-)
> >
> > --- a/drivers/idle/intel_idle.c
> > +++ b/drivers/idle/intel_idle.c
> > @@ -126,26 +126,9 @@ static __cpuidle int intel_idle(struct c
> >         struct cpuidle_state *state = &drv->states[index];
> >         unsigned long eax = flg2MWAIT(state->flags);
> >         unsigned long ecx = 1; /* break on interrupt flag */
> > -       bool tick;
> > -
> > -       if (!static_cpu_has(X86_FEATURE_ARAT)) {
> > -               /*
> > -                * Switch over to one-shot tick broadcast if the target C-state
> > -                * is deeper than C1.
> > -                */
> > -               if ((eax >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) {
> > -                       tick = true;
> > -                       tick_broadcast_enter();
> > -               } else {
> > -                       tick = false;
> > -               }
> > -       }
> >
> >         mwait_idle_with_hints(eax, ecx);
> >
> > -       if (!static_cpu_has(X86_FEATURE_ARAT) && tick)
> > -               tick_broadcast_exit();
> > -
> >         return index;
> >  }
> >
> > @@ -1460,6 +1443,23 @@ static bool __init intel_idle_verify_cst
> >         return true;
> >  }
> >
> > +static bool __init intel_idle_state_needs_timer_stop(struct cpuidle_state *state)
> > +{
> > +       unsigned long eax = flg2MWAIT(state->flags);
> > +
> > +       if (boot_cpu_has(X86_FEATURE_ARAT))
> > +               return false;
> > +
> > +       /*
> > +        * Switch over to one-shot tick broadcast if the target C-state
> > +        * is deeper than C1.
> > +        */
> > +       if ((eax >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK)
> > +               return true;
> > +
> > +       return false;
> > +}
> > +
> >  static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
> >  {
> >         int cstate;
> > @@ -1507,6 +1507,9 @@ static void __init intel_idle_init_cstat
> >                      !(cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_ALWAYS_ENABLE)))
> >                         drv->states[drv->state_count].flags |= CPUIDLE_FLAG_OFF;
> >
> > +               if (intel_idle_state_needs_timer_stop(&drv->states[drv->state_count]))
> > +                       drv->states[drv->state_count].flags |= CPUIDLE_FLAG_TIMER_STOP;
> > +
> >                 drv->state_count++;
> >         }
> 
> This doesn't cover the ACPI case AFAICS.

aa6b43d57f99 ("ACPI: processor: Use CPUIDLE_FLAG_TIMER_STOP")

did that, no?