linux-kernel - Re: [PATCH 2/4] ACPI: PM: Remove redundant cache flushing

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Date:   Fri, 17 Dec 2021 19:04:30 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Luck <tony.luck@...el.com>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH 2/4] ACPI: PM: Remove redundant cache flushing

On Thu, Dec 9, 2021 at 2:32 PM Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
>
> On Tue, Dec 07, 2021 at 05:35:38PM +0100, Rafael J. Wysocki wrote:
> > I don't think this is needed for S2, because the function doesn't do
> > anything low-level in that case and simply returns (IOW, S2 isn't
> > really supported).
>
> Updated patch is below. Does it look good?

It does, and so applied as 5.17 material with some minor edits in the changelog.

Thanks!

> From 5eb4ec7d8dd463ba186b779dcef2a802d999c59c Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Date: Thu, 9 Dec 2021 16:08:02 +0300
> Subject: [PATCH 1/2] ACPI: PM: Remove redundant cache flushing
>
> ACPICA code takes care about cache flushing on S1/S2/S3 in
> acpi_hw_extended_sleep() and acpi_hw_legacy_sleep().
>
> acpi_suspend_enter() calls into ACPICA code via acpi_enter_sleep_state()
> for S1 or x86_acpi_suspend_lowlevel() for S3.
>
> acpi_sleep_prepare() call tree:
>   __acpi_pm_prepare()
>     acpi_pm_prepare()
>       acpi_suspend_ops::prepare_late()
>       acpi_hibernation_ops::pre_snapshot()
>       acpi_hibernation_ops::prepare()
>     acpi_suspend_begin_old()
>       acpi_suspend_begin_old::begin()
>   acpi_hibernation_begin_old()
>     acpi_hibernation_ops_old::acpi_hibernation_begin_old()
>   acpi_power_off_prepare()
>     pm_power_off_prepare()
>
> Hibernation (S4) and Power Off (S5) don't require cache flushing. So,
> the only interesting callsites are acpi_suspend_ops::prepare_late() and
> acpi_suspend_begin_old::begin(). Both of them have cache flush on
> ->enter() operation in acpi_suspend_enter().
>
> Remove redundant ACPI_FLUSH_CPU_CACHE() in acpi_sleep_prepare() and
> acpi_suspend_enter().
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  drivers/acpi/sleep.c | 3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/drivers/acpi/sleep.c b/drivers/acpi/sleep.c
> index eaa47753b758..5ca6c223ba3d 100644
> --- a/drivers/acpi/sleep.c
> +++ b/drivers/acpi/sleep.c
> @@ -73,7 +73,6 @@ static int acpi_sleep_prepare(u32 acpi_state)
>                 acpi_set_waking_vector(acpi_wakeup_address);
>
>         }
> -       ACPI_FLUSH_CPU_CACHE();
>  #endif
>         pr_info("Preparing to enter system sleep state S%d\n", acpi_state);
>         acpi_enable_wakeup_devices(acpi_state);
> @@ -566,8 +565,6 @@ static int acpi_suspend_enter(suspend_state_t pm_state)
>         u32 acpi_state = acpi_target_sleep_state;
>         int error;
>
> -       ACPI_FLUSH_CPU_CACHE();
> -
>         trace_suspend_resume(TPS("acpi_suspend"), acpi_state, true);
>         switch (acpi_state) {
>         case ACPI_STATE_S1:
> --
>  Kirill A. Shutemov