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KVM: x86: make backwards_tsc_observed a per-VM variable

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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>
This commit is contained in:
Ladi Prosek
2017-06-26 09:56:43 +02:00
committed by Radim Krčmář
parent 286de8f6ac
commit a826faf108
2 changed files with 3 additions and 4 deletions
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arch/x86/include/asm/kvm_host.h
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@@ -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;