diff options
| author | Jan Stancek <jstancek@redhat.com> | 2019-09-08 00:50:40 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2019-09-08 09:01:15 +0200 |
| commit | afa8b475c1aec185a8e106c48b3832e0b88bc2de (patch) | |
| tree | 31c65e7de8fcd3604497fcd8bf93b65cc3ed6cf7 | |
| parent | e16c2983fba0fa6763e43ad10916be35e3d8dc05 (diff) | |
x86/timer: Force PIT initialization when !X86_FEATURE_ARAT
KVM guests with commit c8c4076723da ("x86/timer: Skip PIT initialization on
modern chipsets") applied to guest kernel have been observed to have
unusually higher CPU usage with symptoms of increase in vm exits for HLT
and MSW_WRITE (MSR_IA32_TSCDEADLINE).
This is caused by older QEMUs lacking support for X86_FEATURE_ARAT. lapic
clock retains CLOCK_EVT_FEAT_C3STOP and nohz stays inactive. There's no
usable broadcast device either.
Do the PIT initialization if guest CPU lacks X86_FEATURE_ARAT. On real
hardware it shouldn't matter as ARAT and DEADLINE come together.
Fixes: c8c4076723da ("x86/timer: Skip PIT initialization on modern chipsets")
Signed-off-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| -rw-r--r-- | arch/x86/kernel/apic/apic.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c index dba2828b779a..f91b3ff9dc03 100644 --- a/arch/x86/kernel/apic/apic.c +++ b/arch/x86/kernel/apic/apic.c @@ -834,6 +834,10 @@ bool __init apic_needs_pit(void) if (!boot_cpu_has(X86_FEATURE_APIC)) return true; + /* Virt guests may lack ARAT, but still have DEADLINE */ + if (!boot_cpu_has(X86_FEATURE_ARAT)) + return true; + /* Deadline timer is based on TSC so no further PIT action required */ if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER)) return false; |