diff mbox series

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

Message ID 20220919101521.139727471@infradead.org (mailing list archive)
State Handled Elsewhere, archived
Headers show
Series cpuidle,rcu: Clean up the mess | expand

Commit Message

Peter Zijlstra Sept. 19, 2022, 9:59 a.m. UTC
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>
---
 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(-)

Comments

Ulf Hansson Oct. 4, 2022, 11:03 a.m. UTC | #1
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
Ulf Hansson Oct. 4, 2022, 11:43 a.m. UTC | #2
On Tue, 4 Oct 2022 at 13:03, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
> 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>

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
Peter Zijlstra Nov. 16, 2022, 3:29 p.m. UTC | #3
Sorry; things keep getting in the way of finishing this :/

As such, I need a bit of time to get on-track again..

On Tue, Oct 04, 2022 at 01:03:57PM +0200, Ulf Hansson wrote:

> > --- 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.

I'm not quite sure I see how. AFAICT this condition above implies
acpi_processor_ffh_lpi_enter() gets called, no?

Which in turn is an unconditional __CPU_PM_CPU_IDLE_ENTER() user, so
even if idx==0, it ends up in ct_idle_{enter,exit}().

> 
> >                 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.

True.

> 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?

As per the below?

> 
> >                 .enter                  = arm_enter_idle_state,
> >                 .exit_latency           = 1,
> >                 .target_residency       = 1,

> > --- 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?

Yes, if we ensure idx==0 never has RCU_IDLE set then these must be
removed.

> >                 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();                                  \
> >         }                                                               \
> >

So the basic premise is that everything that needs RCU inside the idle
callback must set CPUIDLE_FLAG_RCU_IDLE and by doing that promise to
call ct_idle_{enter,exit}() themselves.

Setting RCU_IDLE is required when there is RCU usage, however even if
there is no RCU usage, setting RCU_IDLE is fine, as long as
ct_idle_{enter,exit}() then get called.


So does the below (delta) look better to you?

--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -1218,7 +1218,7 @@ 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)
+		if (i != 0 && lpi->entry_method == ACPI_CSTATE_FFH)
 			state->flags |= CPUIDLE_FLAG_RCU_IDLE;
 		state->enter = acpi_idle_lpi_enter;
 		drv->safe_state_index = i;
--- a/drivers/cpuidle/cpuidle-arm.c
+++ b/drivers/cpuidle/cpuidle-arm.c
@@ -53,7 +53,7 @@ static struct cpuidle_driver arm_idle_dr
 	 * handler for idle state index 0.
 	 */
 	.states[0] = {
-		.flags			= CPUIDLE_FLAG_RCU_IDLE,
+		.flags			= 0,
 		.enter                  = arm_enter_idle_state,
 		.exit_latency           = 1,
 		.target_residency       = 1,
--- a/drivers/cpuidle/cpuidle-psci.c
+++ b/drivers/cpuidle/cpuidle-psci.c
@@ -357,7 +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].flags = 0;
 	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
@@ -72,7 +72,7 @@ static struct cpuidle_driver qcom_spm_id
 	.owner = THIS_MODULE,
 	.states[0] = {
 		.enter			= spm_enter_idle_state,
-		.flags			= CPUIDLE_FLAG_RCU_IDLE,
+		.flags			= 0,
 		.exit_latency		= 1,
 		.target_residency	= 1,
 		.power_usage		= UINT_MAX,
--- a/drivers/cpuidle/cpuidle-riscv-sbi.c
+++ b/drivers/cpuidle/cpuidle-riscv-sbi.c
@@ -337,7 +337,7 @@ 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].flags = 0;
 	drv->states[0].enter = sbi_cpuidle_enter_state;
 	drv->states[0].exit_latency = 1;
 	drv->states[0].target_residency = 1;
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -282,9 +282,7 @@ extern s64 cpuidle_governor_latency_req(
 	int __ret = 0;							\
 									\
 	if (!idx) {							\
-		ct_idle_enter();					\
 		cpu_do_idle();						\
-		ct_idle_exit();						\
 		return idx;						\
 	}								\
 									\
Ulf Hansson Nov. 22, 2022, 4:04 p.m. UTC | #4
On Wed, 16 Nov 2022 at 16:29, Peter Zijlstra <peterz@infradead.org> wrote:
>
>
> Sorry; things keep getting in the way of finishing this :/
>
> As such, I need a bit of time to get on-track again..
>
> On Tue, Oct 04, 2022 at 01:03:57PM +0200, Ulf Hansson wrote:
>
> > > --- 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.
>
> I'm not quite sure I see how. AFAICT this condition above implies
> acpi_processor_ffh_lpi_enter() gets called, no?
>
> Which in turn is an unconditional __CPU_PM_CPU_IDLE_ENTER() user, so
> even if idx==0, it ends up in ct_idle_{enter,exit}().

Seems like I was overlooking something here, you are right, this
shouldn't really be a problem.

>
> >
> > >                 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.
>
> True.
>
> > 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?
>
> As per the below?
>
> >
> > >                 .enter                  = arm_enter_idle_state,
> > >                 .exit_latency           = 1,
> > >                 .target_residency       = 1,
>
> > > --- 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?
>
> Yes, if we ensure idx==0 never has RCU_IDLE set then these must be
> removed.
>
> > >                 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();                                  \
> > >         }                                                               \
> > >
>
> So the basic premise is that everything that needs RCU inside the idle
> callback must set CPUIDLE_FLAG_RCU_IDLE and by doing that promise to
> call ct_idle_{enter,exit}() themselves.
>
> Setting RCU_IDLE is required when there is RCU usage, however even if
> there is no RCU usage, setting RCU_IDLE is fine, as long as
> ct_idle_{enter,exit}() then get called.

Right, I was thinking that it could make sense to shrink the window
for users getting this wrong. In other words, we shouldn't set the
CPUIDLE_FLAG_RCU_IDLE unless we really need to.

And as I said, consistent behaviour is also nice to have.

>
>
> So does the below (delta) look better to you?

Yes, it does!

Although, one minor comment below.

>
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -1218,7 +1218,7 @@ 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)
> +               if (i != 0 && lpi->entry_method == ACPI_CSTATE_FFH)
>                         state->flags |= CPUIDLE_FLAG_RCU_IDLE;
>                 state->enter = acpi_idle_lpi_enter;
>                 drv->safe_state_index = i;
> --- a/drivers/cpuidle/cpuidle-arm.c
> +++ b/drivers/cpuidle/cpuidle-arm.c
> @@ -53,7 +53,7 @@ static struct cpuidle_driver arm_idle_dr
>          * handler for idle state index 0.
>          */
>         .states[0] = {
> -               .flags                  = CPUIDLE_FLAG_RCU_IDLE,
> +               .flags                  = 0,

Nitpick: I don't think we need to explicitly clear the flag, as it
should already be zeroed by the compiler from its static declaration.
Right?

>                 .enter                  = arm_enter_idle_state,
>                 .exit_latency           = 1,
>                 .target_residency       = 1,
> --- a/drivers/cpuidle/cpuidle-psci.c
> +++ b/drivers/cpuidle/cpuidle-psci.c
> @@ -357,7 +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].flags = 0;
>         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
> @@ -72,7 +72,7 @@ static struct cpuidle_driver qcom_spm_id
>         .owner = THIS_MODULE,
>         .states[0] = {
>                 .enter                  = spm_enter_idle_state,
> -               .flags                  = CPUIDLE_FLAG_RCU_IDLE,
> +               .flags                  = 0,
>                 .exit_latency           = 1,
>                 .target_residency       = 1,
>                 .power_usage            = UINT_MAX,
> --- a/drivers/cpuidle/cpuidle-riscv-sbi.c
> +++ b/drivers/cpuidle/cpuidle-riscv-sbi.c
> @@ -337,7 +337,7 @@ 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].flags = 0;
>         drv->states[0].enter = sbi_cpuidle_enter_state;
>         drv->states[0].exit_latency = 1;
>         drv->states[0].target_residency = 1;
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -282,9 +282,7 @@ extern s64 cpuidle_governor_latency_req(
>         int __ret = 0;                                                  \
>                                                                         \
>         if (!idx) {                                                     \
> -               ct_idle_enter();                                        \
>                 cpu_do_idle();                                          \
> -               ct_idle_exit();                                         \
>                 return idx;                                             \
>         }                                                               \
>                                                                         \

Kind regards
Uffe
diff mbox series

Patch

--- 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;
 		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,
 		.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();					\
 		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();					\
 	}								\