Re: [PATCH v2 12/44] cpuidle,dt: Push RCU-idle into driver

[Ulf Hansson <ulf.hansson@linaro.org>]

On Mon, 19 Sept 2022 at 12:18, Peter Zijlstra <peterz@infradead.org> wrote:
>
> Doing RCU-idle outside the driver, only to then temporarily enable it
> again before going idle is daft.
>
> Notably: this converts all dt_init_idle_driver() and
> __CPU_PM_CPU_IDLE_ENTER() users for they are inextrably intertwined.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

Kind regards
Uffe

> ---
>  arch/arm/mach-omap2/cpuidle34xx.c    |    4 ++--
>  drivers/acpi/processor_idle.c        |    2 ++
>  drivers/cpuidle/cpuidle-arm.c        |    1 +
>  drivers/cpuidle/cpuidle-big_little.c |    8 ++++++--
>  drivers/cpuidle/cpuidle-psci.c       |    1 +
>  drivers/cpuidle/cpuidle-qcom-spm.c   |    1 +
>  drivers/cpuidle/cpuidle-riscv-sbi.c  |    1 +
>  drivers/cpuidle/dt_idle_states.c     |    2 +-
>  include/linux/cpuidle.h              |    4 ++++
>  9 files changed, 19 insertions(+), 5 deletions(-)
>
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -1200,6 +1200,8 @@ static int acpi_processor_setup_lpi_stat
>                 state->target_residency = lpi->min_residency;
>                 if (lpi->arch_flags)
>                         state->flags |= CPUIDLE_FLAG_TIMER_STOP;
> +               if (lpi->entry_method == ACPI_CSTATE_FFH)
> +                       state->flags |= CPUIDLE_FLAG_RCU_IDLE;

I assume the state index here will never be 0?

If not, it may lead to that acpi_processor_ffh_lpi_enter() may trigger
CPU_PM_CPU_IDLE_ENTER_PARAM() to call ct_cpuidle_enter|exit() for an
idle-state that doesn't have the CPUIDLE_FLAG_RCU_IDLE bit set.

>                 state->enter = acpi_idle_lpi_enter;
>                 drv->safe_state_index = i;
>         }
> --- a/drivers/cpuidle/cpuidle-arm.c
> +++ b/drivers/cpuidle/cpuidle-arm.c
> @@ -53,6 +53,7 @@ static struct cpuidle_driver arm_idle_dr
>          * handler for idle state index 0.
>          */
>         .states[0] = {
> +               .flags                  = CPUIDLE_FLAG_RCU_IDLE,

Comparing arm64 and arm32 idle-states/idle-drivers, the $subject
series ends up setting the CPUIDLE_FLAG_RCU_IDLE for the ARM WFI idle
state (state zero), but only for the arm64 and psci cases (mostly
arm64). For arm32 we would need to update the ARM_CPUIDLE_WFI_STATE
too, as that is what most arm32 idle-drivers are using. My point is,
the code becomes a bit inconsistent.

Perhaps it's easier to avoid setting the CPUIDLE_FLAG_RCU_IDLE bit for
all of the ARM WFI idle states, for both arm64 and arm32?

>                 .enter                  = arm_enter_idle_state,
>                 .exit_latency           = 1,
>                 .target_residency       = 1,
> --- a/drivers/cpuidle/cpuidle-big_little.c
> +++ b/drivers/cpuidle/cpuidle-big_little.c
> @@ -64,7 +64,8 @@ static struct cpuidle_driver bl_idle_lit
>                 .enter                  = bl_enter_powerdown,
>                 .exit_latency           = 700,
>                 .target_residency       = 2500,
> -               .flags                  = CPUIDLE_FLAG_TIMER_STOP,
> +               .flags                  = CPUIDLE_FLAG_TIMER_STOP |
> +                                         CPUIDLE_FLAG_RCU_IDLE,
>                 .name                   = "C1",
>                 .desc                   = "ARM little-cluster power down",
>         },
> @@ -85,7 +86,8 @@ static struct cpuidle_driver bl_idle_big
>                 .enter                  = bl_enter_powerdown,
>                 .exit_latency           = 500,
>                 .target_residency       = 2000,
> -               .flags                  = CPUIDLE_FLAG_TIMER_STOP,
> +               .flags                  = CPUIDLE_FLAG_TIMER_STOP |
> +                                         CPUIDLE_FLAG_RCU_IDLE,
>                 .name                   = "C1",
>                 .desc                   = "ARM big-cluster power down",
>         },
> @@ -124,11 +126,13 @@ static int bl_enter_powerdown(struct cpu
>                                 struct cpuidle_driver *drv, int idx)
>  {
>         cpu_pm_enter();
> +       ct_idle_enter();
>
>         cpu_suspend(0, bl_powerdown_finisher);
>
>         /* signals the MCPM core that CPU is out of low power state */
>         mcpm_cpu_powered_up();
> +       ct_idle_exit();
>
>         cpu_pm_exit();
>
> --- a/drivers/cpuidle/cpuidle-psci.c
> +++ b/drivers/cpuidle/cpuidle-psci.c
> @@ -357,6 +357,7 @@ static int psci_idle_init_cpu(struct dev
>          * PSCI idle states relies on architectural WFI to be represented as
>          * state index 0.
>          */
> +       drv->states[0].flags = CPUIDLE_FLAG_RCU_IDLE;
>         drv->states[0].enter = psci_enter_idle_state;
>         drv->states[0].exit_latency = 1;
>         drv->states[0].target_residency = 1;
> --- a/drivers/cpuidle/cpuidle-qcom-spm.c
> +++ b/drivers/cpuidle/cpuidle-qcom-spm.c
> @@ -72,6 +72,7 @@ static struct cpuidle_driver qcom_spm_id
>         .owner = THIS_MODULE,
>         .states[0] = {
>                 .enter                  = spm_enter_idle_state,
> +               .flags                  = CPUIDLE_FLAG_RCU_IDLE,
>                 .exit_latency           = 1,
>                 .target_residency       = 1,
>                 .power_usage            = UINT_MAX,
> --- a/drivers/cpuidle/cpuidle-riscv-sbi.c
> +++ b/drivers/cpuidle/cpuidle-riscv-sbi.c
> @@ -332,6 +332,7 @@ static int sbi_cpuidle_init_cpu(struct d
>         drv->cpumask = (struct cpumask *)cpumask_of(cpu);
>
>         /* RISC-V architectural WFI to be represented as state index 0. */
> +       drv->states[0].flags = CPUIDLE_FLAG_RCU_IDLE;
>         drv->states[0].enter = sbi_cpuidle_enter_state;
>         drv->states[0].exit_latency = 1;
>         drv->states[0].target_residency = 1;
> --- a/drivers/cpuidle/dt_idle_states.c
> +++ b/drivers/cpuidle/dt_idle_states.c
> @@ -77,7 +77,7 @@ static int init_state_node(struct cpuidl
>         if (err)
>                 desc = state_node->name;
>
> -       idle_state->flags = 0;
> +       idle_state->flags = CPUIDLE_FLAG_RCU_IDLE;
>         if (of_property_read_bool(state_node, "local-timer-stop"))
>                 idle_state->flags |= CPUIDLE_FLAG_TIMER_STOP;
>         /*
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -282,14 +282,18 @@ extern s64 cpuidle_governor_latency_req(
>         int __ret = 0;                                                  \
>                                                                         \
>         if (!idx) {                                                     \
> +               ct_idle_enter();                                        \

According to my comment above, we should then drop these calls to
ct_idle_enter and ct_idle_exit() here. Right?

>                 cpu_do_idle();                                          \
> +               ct_idle_exit();                                         \
>                 return idx;                                             \
>         }                                                               \
>                                                                         \
>         if (!is_retention)                                              \
>                 __ret =  cpu_pm_enter();                                \
>         if (!__ret) {                                                   \
> +               ct_idle_enter();                                        \
>                 __ret = low_level_idle_enter(state);                    \
> +               ct_idle_exit();                                         \
>                 if (!is_retention)                                      \
>                         cpu_pm_exit();                                  \
>         }                                                               \
>

Kind regards
Uffe