On Tue, 4 Oct 2022 at 13:03, Ulf Hansson [off-list ref] wrote:

On Mon, 19 Sept 2022 at 12:18, Peter Zijlstra [off-list ref] wrote:

quoted

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 <redacted>

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

Kind regards
Uffe

quoted

---
 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.

quoted

                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?

quoted

                .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?

quoted

                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