[PATCH] x86: kvm: fix unstable_tsc boot

Andrew Jones
2014-02-24T15:42:39Z

When the tsc is marked unstable on the host it causes global clock
updates to be requested each time a vcpu is loaded, nearly halting
all progress on guests with a large number of vcpus.

Fix this by only requesting a local clock update unless the vcpu
is migrating to another cpu.

Signed-off-by: Andrew Jones <drjones@redhat.com>
---
arch/x86/kvm/x86.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6530019116b0d..ea716a162b4a3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2781,15 +2781,18 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
vcpu->arch.last_guest_tsc);
kvm_x86_ops->write_tsc_offset(vcpu, offset);
vcpu->arch.tsc_catchup = 1;
+ set_bit(KVM_REQ_CLOCK_UPDATE, &vcpu->requests);
}
+ }
+
+ if (unlikely(vcpu->cpu != cpu)) {
/*
* On a host with synchronized TSC, there is no need to update
* kvmclock on vcpu->cpu migration
*/
if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1)
kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
- if (vcpu->cpu != cpu)
- kvm_migrate_timers(vcpu);
+ kvm_migrate_timers(vcpu);
vcpu->cpu = cpu;
}

--
1.8.1.4