On Wed, Oct 9, 2024 at 9:20 AM Zhang Rui rui.zhang@intel.com wrote:
This 12-year-old bug prevents some modern processors from achieving maximum power savings during suspend. For example, Lunar Lake systems gets 0% package C-states during suspend to idle and this causes energy star compliance tests to fail.
According to Intel SDM, for the local APIC timer,
- "The initial-count register is a read-write register. A write of 0 to the initial-count register effectively stops the local APIC timer, in both one-shot and periodic mode."
- "In TSC deadline mode, writes to the initial-count register are ignored; and current-count register always reads 0. Instead, timer behavior is controlled using the IA32_TSC_DEADLINE MSR." "In TSC-deadline mode, writing 0 to the IA32_TSC_DEADLINE MSR disarms the local-APIC timer."
Stop the TSC Deadline timer in lapic_timer_shutdown() by writing 0 to MSR_IA32_TSC_DEADLINE.
Cc: stable@vger.kernel.org Fixes: 279f1461432c ("x86: apic: Use tsc deadline for oneshot when available") Signed-off-by: Zhang Rui rui.zhang@intel.com
Acked-by: Rafael J. Wysocki rafael.j.wysocki@intel.com
x86 folks, this is quite nasty, so please make it high-prio.
Alternatively, I can take it through the PM tree.
Changes since V1
- improve changelog
arch/x86/kernel/apic/apic.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c index 6513c53c9459..d1006531729a 100644 --- a/arch/x86/kernel/apic/apic.c +++ b/arch/x86/kernel/apic/apic.c @@ -441,6 +441,10 @@ static int lapic_timer_shutdown(struct clock_event_device *evt) v |= (APIC_LVT_MASKED | LOCAL_TIMER_VECTOR); apic_write(APIC_LVTT, v); apic_write(APIC_TMICT, 0);
if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER))wrmsrl(MSR_IA32_TSC_DEADLINE, 0);return 0;}
-- 2.34.1