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

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

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