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

From: Ulf Hansson
Date: Tue Oct 04 2022 - 07:44:43 EST

On Tue, 4 Oct 2022 at 13:03, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>
> 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>

This was not (yet) my intention. Please have a look at the comments I
provided below.

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