linux-kernel - Re: [PATCH] x86/ACPI/State: Optimize C3 entry on AMD CPUs

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Date:   Wed, 1 Sep 2021 14:45:15 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Deepak Sharma <deesharm@....com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Deepak Sharma <deepak.sharma@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:SUSPEND TO RAM" <linux-pm@...r.kernel.org>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/ACPI/State: Optimize C3 entry on AMD CPUs

On Wed, Sep 1, 2021 at 4:14 AM Deepak Sharma <deesharm@....com> wrote:
>
>
> On 8/25/21 11:07 AM, Rafael J. Wysocki wrote:
> > On Thu, Aug 19, 2021 at 2:43 AM Deepak Sharma <deepak.sharma@....com> wrote:
> >> AMD CPU which support C3 shares cache. Its not necessary to flush the
> >> caches in software before entering C3. This will cause performance drop
> >> for the cores which share some caches. ARB_DIS is not used with current
> >> AMD C state implementation. So set related flags correctly.
> >>
> >> Signed-off-by: Deepak Sharma <deepak.sharma@....com>
> > Applied as 5.15 material under the edited subject "x86: ACPI: cstate:
> > Optimize C3 entry on AMD CPUs", thanks!
>
> I might need to send subsequent patch for this. Can you please point me
> to git and branch where this has been merged.

git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next

> >> ---
> >>   arch/x86/kernel/acpi/cstate.c | 15 +++++++++++++++
> >>   1 file changed, 15 insertions(+)
> >>
> >> diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
> >> index 7de599eba7f0..62a5986d625a 100644
> >> --- a/arch/x86/kernel/acpi/cstate.c
> >> +++ b/arch/x86/kernel/acpi/cstate.c
> >> @@ -79,6 +79,21 @@ void acpi_processor_power_init_bm_check(struct acpi_processor_flags *flags,
> >>                   */
> >>                  flags->bm_control = 0;
> >>          }
> >> +       if (c->x86_vendor == X86_VENDOR_AMD) {
> >> +               /*
> >> +                * For all AMD CPUs that support C3, caches should not be
> >> +                * flushed by software while entering C3 type state. Set
> >> +                * bm->check to 1 so that kernel doesn't need to execute
> >> +                * cache flush operation.
> >> +                */
> >> +               flags->bm_check = 1;
> >> +               /*
> >> +                * In current AMD C state implementation ARB_DIS is no longer
> >> +                * used. So set bm_control to zero to indicate ARB_DIS is not
> >> +                * required while entering C3 type state.
> >> +                */
> >> +               flags->bm_control = 0;
> >> +       }
> >>   }
> >>   EXPORT_SYMBOL(acpi_processor_power_init_bm_check);
> >>
> >> --
> >> 2.25.1
> >>