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authorJan Stancek <jstancek@redhat.com>2019-09-08 00:50:40 +0200
committerThomas Gleixner <tglx@linutronix.de>2019-09-08 09:01:15 +0200
commitafa8b475c1aec185a8e106c48b3832e0b88bc2de (patch)
tree31c65e7de8fcd3604497fcd8bf93b65cc3ed6cf7 /arch/x86/kernel/apic
parente16c2983fba0fa6763e43ad10916be35e3d8dc05 (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>
Diffstat (limited to 'arch/x86/kernel/apic')
-rw-r--r--arch/x86/kernel/apic/apic.c4
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;