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

["Rafael J. Wysocki" <rafael@kernel.org>]

On Mon, Nov 23, 2020 at 2:46 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> 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?

Nope.

intel_idle_init_cstates_acpi() needs to be updated too as it doesn't
pick up the flags automatically.  It looks like CPUIDLE_FLAG_RCU_IDLE
needs to be copied too.