KVM: x86: make backwards_tsc_observed a per-VM variable (a826faf1) · Commits · 戴 / test

The backwards_tsc_observed global introduced in commit 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>

arch/x86/include/asm/kvm_host.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -803,6 +803,7 @@ struct kvm_arch {
		int audit_point;
		#endif

		bool backwards_tsc_observed;
		bool boot_vcpu_runs_old_kvmclock;
		u32 bsp_vcpu_id;

arch/x86/kvm/x86.c

+2 −4

Original line number	Diff line number	Diff line
		@@ -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;

		#define KVM_NR_SHARED_MSRS 16

		struct kvm_shared_msrs_global {
		@@ -1719,7 +1717,7 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm)
		&ka->master_cycle_now);

		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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