On Wed, 2024-09-25 at 16:24 -0700, Ankur Arora wrote:
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>
>
> Add architectural support for the cpuidle-haltpoll driver by defining
> arch_haltpoll_*(). Also define ARCH_CPUIDLE_HALTPOLL to allow
> cpuidle-haltpoll to be selected.
>
> Haltpoll uses poll_idle() to do the actual polling. This in turn
> uses smp_cond_load*() to wait until there's a specific store to
> a cacheline.
> In the edge case -- no stores to the cacheline and no interrupt --
> the event-stream provides the terminating condition ensuring we
> don't wait forever. But because the event-stream runs at a fixed
> frequency (configured at 10kHz) haltpoll might spend more time in
> the polling stage than specified by cpuidle_poll_time().
>
> This would only happen in the last iteration, since overshooting the
> poll_limit means the governor will move out of the polling stage.
>
> Tested-by: Haris Okanovic <harisokn@xxxxxxxxxx>
> Tested-by: Misono Tomohiro <misono.tomohiro@xxxxxxxxxxx>
> Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
> ---
> arch/arm64/Kconfig | 6 ++++++
> arch/arm64/include/asm/cpuidle_haltpoll.h | 24 +++++++++++++++++++++++
> 2 files changed, 30 insertions(+)
> create mode 100644 arch/arm64/include/asm/cpuidle_haltpoll.h
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index ef9c22c3cff2..5fc99eba22b2 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -2415,6 +2415,12 @@ config ARCH_HIBERNATION_HEADER
> config ARCH_SUSPEND_POSSIBLE
> def_bool y
>
> +config ARCH_CPUIDLE_HALTPOLL
> + bool "Enable selection of the cpuidle-haltpoll driver"
> + help
> + cpuidle-haltpoll allows for adaptive polling based on
> + current load before entering the idle state.
> +
> endmenu # "Power management options"
>
> menu "CPU Power Management"
> diff --git a/arch/arm64/include/asm/cpuidle_haltpoll.h b/arch/arm64/include/asm/cpuidle_haltpoll.h
> new file mode 100644
> index 000000000000..91f0be707629
> --- /dev/null
> +++ b/arch/arm64/include/asm/cpuidle_haltpoll.h
> @@ -0,0 +1,24 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _ARCH_HALTPOLL_H
> +#define _ARCH_HALTPOLL_H
> +
> +static inline void arch_haltpoll_enable(unsigned int cpu) { }
> +static inline void arch_haltpoll_disable(unsigned int cpu) { }
> +
> +static inline bool arch_haltpoll_want(bool force)
> +{
> + /*
> + * Enabling haltpoll requires two things:
> + *
> + * - Event stream support to provide a terminating condition to the
> + * WFE in the poll loop.
I missed this earlier: Why did you drop arch_timer_evtstrm_available()?
> + *
> + * - KVM support for arch_haltpoll_enable(), arch_haltpoll_disable().
> + *
> + * Given that the second is missing, only allow force loading for
> + * haltpoll.
> + */
> + return force;
> +}
> +#endif
> --
> 2.43.5
>
