linux-kernel - Re: [PATCH 09/10] x86: Remove the current_clr

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Message-ID: <CAJZ5v0hWjbp5ALCkiPP0=7CmDmWJzWE-zh2CP6EFLSbShTnVcQ@mail.gmail.com>
Date:   Fri, 11 Aug 2023 19:41:48 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Len Brown <lenb@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: Re: [PATCH 09/10] x86: Remove the current_clr_polling() call upon
 mwait exit

On Fri, Aug 11, 2023 at 7:01 PM Frederic Weisbecker <frederic@...nel.org> wrote:
>
> mwait_idle_with_hints() is mostly called from cpuidle which already sets
> back TIF_NR_POLLING and fold TIF_NEED_RESCHED if necessary.
>
> The only non-cpuidle caller is power_saving_thread() which acts as an idle
> loop and is the only reason why mwait_idle_with_hints() carries a costly
> fully ordered atomic operation upon idle exit.
>
> Make this overhead proper to power_saving_thread() instead which already
> duplicates quite some cpuidle code.
>
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>

Acked-by: Rafael J. Wysocki <rafael@...nel.org>

> ---
>  arch/x86/include/asm/mwait.h | 1 -
>  drivers/acpi/acpi_pad.c      | 1 +
>  2 files changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
> index 920426d691ce..c1be3775b94a 100644
> --- a/arch/x86/include/asm/mwait.h
> +++ b/arch/x86/include/asm/mwait.h
> @@ -134,7 +134,6 @@ static __always_inline void mwait_idle_with_hints(unsigned long eax, unsigned lo
>                         }
>                 }
>         }
> -       current_clr_polling();
>  }
>
>  /*
> diff --git a/drivers/acpi/acpi_pad.c b/drivers/acpi/acpi_pad.c
> index 7a453c5ff303..5a44afafe185 100644
> --- a/drivers/acpi/acpi_pad.c
> +++ b/drivers/acpi/acpi_pad.c
> @@ -174,6 +174,7 @@ static int power_saving_thread(void *data)
>                         stop_critical_timings();
>
>                         mwait_idle_with_hints(power_saving_mwait_eax, 1);
> +                       current_clr_polling();
>
>                         start_critical_timings();
>                         tick_broadcast_exit();
> --
> 2.34.1
>