linux-kernel - Re: [PATCH 15/20] ACPICA: executer/exsystem: Warn about sleeps greater than 10 ms

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Date:   Sat, 21 May 2022 18:11:31 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Bob Moore <robert.moore@...el.com>
Cc:     Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Paul Menzel <pmenzel@...gen.mpg.de>
Subject: Re: [PATCH 15/20] ACPICA: executer/exsystem: Warn about sleeps
 greater than 10 ms

On Mon, Apr 11, 2022 at 9:04 PM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> From: Paul Menzel <pmenzel@...gen.mpg.de>
>
> ACPICA commit 2a0d1d475e7ea1c815bee1e0692d81db9a7c909c
>
> Quick boottime is important, so warn about sleeps greater than 10 ms.
>
> Distribution Linux kernels reach initrd in 350 ms, so excessive delays
> should be called out. 10 ms is chosen randomly, but three of such delays
> would already make up ten percent of the boottime.
>
> Link: https://github.com/acpica/acpica/commit/2a0d1d47
> Signed-off-by: Bob Moore <robert.moore@...el.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

I have decided to revert this, because it spams logs with unuseful
warnings on many production systems.

Power management AML uses sleeps above 10 ms for PCI spec compliance
and polling is not useful in those cases.

I will submit an analogous revert for upstream ACPICA.

> ---
>  exsystem.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff -Nurp linux.before_name/drivers/acpi/acpica/exsystem.c linux.after_name/drivers/acpi/acpica/exsystem.c
> --- linux.before_name/drivers/acpi/acpica/exsystem.c    2022-04-01 18:26:54.958046947 +0200
> +++ linux.after_name/drivers/acpi/acpica/exsystem.c     2022-04-01 18:26:51.760086923 +0200
> @@ -170,6 +170,16 @@ acpi_status acpi_ex_system_do_sleep(u64
>         acpi_ex_exit_interpreter();
>
>         /*
> +        * Warn users about excessive sleep times, so ASL code can be improved to
> +        * use polling or similar techniques.
> +        */
> +       if (how_long_ms > 10) {
> +               ACPI_WARNING((AE_INFO,
> +                             "Firmware issue: Excessive sleep time (%llu ms > 10 ms) in ACPI Control Method",
> +                             how_long_us));
> +       }
> +
> +       /*
>          * For compatibility with other ACPI implementations and to prevent
>          * accidental deep sleeps, limit the sleep time to something reasonable.
>          */
>
>
>