Re: [PATCH 3/4] ACPI: processor idle: Only flush cache on entering C3

Peter Zijlstra
2021-12-06T15:08:22Z

On Mon, Dec 06, 2021 at 03:29:51PM +0300, Kirill A. Shutemov wrote:
> According to the ACPI spec v6.4, section 8.2, cache flushing required
> on entering C3 power state.
>
> Avoid flushing cache on entering other power states.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> drivers/acpi/processor_idle.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index 76ef1bcc8848..01495aca850e 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -567,7 +567,8 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
> {
> struct acpi_processor_cx *cx = per_cpu(acpi_cstate[index], dev->cpu);
>
> - ACPI_FLUSH_CPU_CACHE();
> + if (cx->type == ACPI_STATE_C3)
> + ACPI_FLUSH_CPU_CACHE();
>

acpi_idle_enter() already does this, acpi_idle_enter_s2idle() has it
confused again,

Also, I think acpi_idle_enter() does it too late; consider
acpi_idle_enter_mb(). Either that or the BM crud needs more comments.