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But > > this guest-friendly behavior causes performance problems on bare metal. > > So there's a 'virt_spin_lock_key' static key to switch between the two > > modes. > > > > The static key is always enabled by default (run in guest mode) and > > should be disabled for bare metal (and in some guests that want native > > behavior). > > > > Performance drop is reported when running encode/decode workload and > > BenchSEE cache sub-workload. > > Bisect points to commit ce0a1b608bfc ("x86/paravirt: Silence unused > > native_pv_lock_init() function warning"). When CONFIG_PARAVIRT_SPINLOCKS > > is disabled the virt_spin_lock_key is incorrectly set to true on bare > > metal. The qspinlock degenerates to test-and-set spinlock, which > > decrease the performance on bare metal. > > > > Set the default value of virt_spin_lock_key to false. If booting in a VM, > > enable this key. Later during the VM initialization, if other > > high-efficient spinlock is preferred(paravirt-spinlock eg), the > > virt_spin_lock_key is disabled accordingly. The relation is described as > > below: > > > > X86_FEATURE_HYPERVISOR Y Y Y N > > CONFIG_PARAVIRT_SPINLOCKS Y Y N Y/N > > PV spinlock Y N N Y/N > > > > virt_spin_lock_key N N Y N > > > > -DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key); > > +DEFINE_STATIC_KEY_FALSE(virt_spin_lock_key); > > void __init native_pv_lock_init(void) > > { > > - if (IS_ENABLED(CONFIG_PARAVIRT_SPINLOCKS) && > > Actually now shouldn't the CONFIG_PARAVIRT_SPINLOCKS check be retained? > Otherwise we'll have the virtspinlock enabled even if we are a guest but > CONFIG_PARAVIRT_SPINLOCKS is disabled, no ? > It seems to be the expected behavior? If CONFIG_PARAVIRT_SPINLOCKS is disabled, should the virt_spin_lock_key be enabled in the guest? The previous behavior before commit ce0a1b608bfc ("x86/paravirt: Silence unused native_pv_lock_init() function warning"): kvm_spinlock_init() is NULL if CONFIG_PARAVIRT_SPINLOCKS is disabled, and static_branch_disable(&virt_spin_lock_key) can not be invoked, so the virt_spin_lock_key keeps enabled. thanks, Chenyu