Re: [PATCH 2/5] cpuidle: Introduce CPUIDLE_FLAG_MWAIT

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Dec 06, 2024 at 02:04:05PM +0100, Frederic Weisbecker wrote:
> From: Peter Zijlstra <peterz@infradead.org>
> 
> Provide a way to tell the cpuidle core about states monitoring
> TIF_NEED_RESCHED on the hardware level, monitor/mwait users being the
> only examples in use.
> 
> This will allow cpuidle core to manage TIF_NR_POLLING on behalf of all
> kinds of TIF_NEED_RESCHED watching states while keeping a necessary
> distinction for the governors between software loops polling on
> TIF_NEED_RESCHED and hardware monitored writes to thread flags.
> 
> [fweisbec: _ Initialize flag from acpi_processor_setup_cstates() instead
>              of acpi_processor_setup_lpi_states(), as the latter seem to
>              be about arm64...
>            _ Rename CPUIDLE_FLAG_NO_IPI to CPUIDLE_FLAG_MWAIT]
> 
> Not-yet-signed-off-by: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> ---
>  drivers/acpi/processor_idle.c | 3 +++
>  drivers/idle/intel_idle.c     | 5 ++++-
>  include/linux/cpuidle.h       | 1 +
>  3 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index 698897b29de2..66cb5536d91e 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -806,6 +806,9 @@ static int acpi_processor_setup_cstates(struct acpi_processor *pr)
>  		if (cx->type == ACPI_STATE_C1 || cx->type == ACPI_STATE_C2)
>  			drv->safe_state_index = count;
>  
> +		if (cx->entry_method == ACPI_CSTATE_FFH)
> +			state->flags |= CPUIDLE_FLAG_MWAIT;
> +
>  		/*
>  		 * Halt-induced C1 is not good for ->enter_s2idle, because it
>  		 * re-enables interrupts on exit.  Moreover, C1 is generally not
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index ac4d8faa3886..d52723fbeb04 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -1787,7 +1787,8 @@ static void __init intel_idle_init_cstates_acpi(struct cpuidle_driver *drv)
>  		if (cx->type > ACPI_STATE_C1)
>  			state->target_residency *= 3;
>  
> -		state->flags = MWAIT2flg(cx->address);
> +		state->flags = MWAIT2flg(cx->address) | CPUIDLE_FLAG_MWAIT;
> +
>  		if (cx->type > ACPI_STATE_C2)
>  			state->flags |= CPUIDLE_FLAG_TLB_FLUSHED;
>  
> @@ -2072,6 +2073,8 @@ static bool __init intel_idle_verify_cstate(unsigned int mwait_hint)
>  
>  static void state_update_enter_method(struct cpuidle_state *state, int cstate)
>  {
> +	state->flags |= CPUIDLE_FLAG_MWAIT;
> +
>  	if (state->flags & CPUIDLE_FLAG_INIT_XSTATE) {
>  		/*
>  		 * Combining with XSTATE with IBRS or IRQ_ENABLE flags
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index a9ee4fe55dcf..b8084617aa27 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -85,6 +85,7 @@ struct cpuidle_state {
>  #define CPUIDLE_FLAG_OFF		BIT(4) /* disable this state by default */
>  #define CPUIDLE_FLAG_TLB_FLUSHED	BIT(5) /* idle-state flushes TLBs */
>  #define CPUIDLE_FLAG_RCU_IDLE		BIT(6) /* idle-state takes care of RCU */
> +#define CPUIDLE_FLAG_MWAIT		BIT(7) /* hardware need_resched() monitoring */
>  
>  struct cpuidle_device_kobj;
>  struct cpuidle_state_kobj;
> -- 
> 2.46.0
>