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

From: Ulf Hansson
Date: Tue Oct 04 2022 - 07:04:56 EST

On Mon, 19 Sept 2022 at 12:18, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>

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

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