linux-kernel - Re: [PATCH 2/2] intel_idle: Fix intel

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Message-ID: <CAJZ5v0hhSO36-m-otWp0vqWNNZFiDWPX-xxK-ninRr2d==QOWA@mail.gmail.com>
Date:   Mon, 23 Nov 2020 11:26:39 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>, svens@...ux.ibm.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] intel_idle: Fix intel_idle() vs tracing

On Fri, Nov 20, 2020 at 12:50 PM Peter Zijlstra <peterz@...radead.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@...radead.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.