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

From: Rafael J. Wysocki
Date: Mon Nov 23 2020 - 05:26:53 EST


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