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

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Message-ID: <20211209133217.omm3mzchsfippwjc@black.fi.intel.com>
Date:   Thu, 9 Dec 2021 16:32:17 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     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 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?

>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