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

[Deepak Sharma]

On 8/25/21 11:07 AM, Rafael J. Wysocki wrote:
> On Thu, Aug 19, 2021 at 2:43 AM Deepak Sharma <deepak.sharma@xxxxxxx> 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@xxxxxxx>
> 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.

> > ---
> >   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