diff options
authorLadi Prosek <lprosek@redhat.com>2017-06-26 09:56:43 +0200
committerRadim Krčmář <rkrcmar@redhat.com>2017-07-13 17:25:39 +0200
commita826faf108e2d855929342268e68c43ba667379a (patch)
parent286de8f6ac9202f1c9012784639156c6ec386eb8 (diff)
KVM: x86: make backwards_tsc_observed a per-VM variable
The backwards_tsc_observed global introduced in commit 16a9602 is never reset to false. If a VM happens to be running while the host is suspended (a common source of the TSC jumping backwards), master clock will never be enabled again for any VM. In contrast, if no VM is running while the host is suspended, master clock is unaffected. This is inconsistent and unnecessarily strict. Let's track the backwards_tsc_observed variable separately and let each VM start with a clean slate. Real world impact: My Windows VMs get slower after my laptop undergoes a suspend/resume cycle. The only way to get the perf back is unloading and reloading the kvm module. Signed-off-by: Ladi Prosek <lprosek@redhat.com> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
2 files changed, 3 insertions, 4 deletions
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1588e9e3dc01..ef37d0dc61bd 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -803,6 +803,7 @@ struct kvm_arch {
int audit_point;
+ bool backwards_tsc_observed;
bool boot_vcpu_runs_old_kvmclock;
u32 bsp_vcpu_id;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ca128a9c9cc4..08aa5e442aa7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -134,8 +134,6 @@ module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR);
static bool __read_mostly vector_hashing = true;
module_param(vector_hashing, bool, S_IRUGO);
-static bool __read_mostly backwards_tsc_observed = false;
struct kvm_shared_msrs_global {
@@ -1719,7 +1717,7 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm)
ka->use_master_clock = host_tsc_clocksource && vcpus_matched
- && !backwards_tsc_observed
+ && !ka->backwards_tsc_observed
&& !ka->boot_vcpu_runs_old_kvmclock;
if (ka->use_master_clock)
@@ -7835,8 +7833,8 @@ int kvm_arch_hardware_enable(void)
if (backwards_tsc) {
u64 delta_cyc = max_tsc - local_tsc;
- backwards_tsc_observed = true;
list_for_each_entry(kvm, &vm_list, vm_list) {
+ kvm->arch.backwards_tsc_observed = true;
kvm_for_each_vcpu(i, vcpu, kvm) {
vcpu->arch.tsc_offset_adjustment += delta_cyc;
vcpu->arch.last_host_tsc = local_tsc;

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