@@ -3275,6 +3275,13 @@
[KNL] Number of legacy pty's. Overwrites compiled-in
default number.
+ pvlock_type= [X86,PV_OPS]
+ Specify the paravirt spinlock type to be used.
+ Options are:
+ queued - native queued spinlock
+ pv - paravirt queued spinlock
+ unfair - simple TATAS unfair lock
+
quiet [KNL] Disable most log messages
r128= [HW,DRM]
@@ -690,6 +690,15 @@ static __always_inline bool pv_vcpu_is_preempted(long cpu)
#endif /* SMP && PARAVIRT_SPINLOCKS */
+enum pv_spinlock_type {
+ locktype_auto = 0,
+ locktype_queued = 1,
+ locktype_paravirt = 2,
+ locktype_unfair = 4,
+};
+
+extern enum pv_spinlock_type pv_spinlock_type;
+
#ifdef CONFIG_X86_32
#define PV_SAVE_REGS "pushl %ecx; pushl %edx;"
#define PV_RESTORE_REGS "popl %edx; popl %ecx;"
@@ -646,6 +646,9 @@ void __init kvm_spinlock_init(void)
if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
return;
+ if (pv_spinlock_type & (locktype_queued|locktype_unfair))
+ return;
+
__pv_init_lock_hash();
pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
@@ -115,11 +115,48 @@ unsigned paravirt_patch_jmp(void *insnbuf, const void *target,
return 5;
}
+/*
+ * The kernel argument "pvlock_type=" can be used to explicitly specify
+ * which type of spinlocks to be used. Currently, there are 3 options:
+ * 1) queued - the native queued spinlock
+ * 2) pv - the paravirt queued spinlock (if CONFIG_PARAVIRT_SPINLOCKS)
+ * 3) unfair - the simple TATAS unfair lock
+ *
+ * If this argument is not specified, the kernel will automatically choose
+ * an appropriate one depending on X86_FEATURE_HYPERVISOR and hypervisor
+ * specific settings.
+ */
+enum pv_spinlock_type __read_mostly pv_spinlock_type = locktype_auto;
+
+static int __init pvlock_setup(char *s)
+{
+ if (!s)
+ return -EINVAL;
+
+ if (!strcmp(s, "queued"))
+ pv_spinlock_type = locktype_queued;
+ else if (!strcmp(s, "pv"))
+ pv_spinlock_type = locktype_paravirt;
+ else if (!strcmp(s, "unfair"))
+ pv_spinlock_type = locktype_unfair;
+ else
+ return -EINVAL;
+
+ pr_info("PV lock type = %s (%d)\n", s, pv_spinlock_type);
+ return 0;
+}
+
+early_param("pvlock_type", pvlock_setup);
+
DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key);
void __init native_pv_lock_init(void)
{
- if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
+ if (pv_spinlock_type == locktype_unfair)
+ return;
+
+ if (!static_cpu_has(X86_FEATURE_HYPERVISOR) ||
+ (pv_spinlock_type == locktype_queued))
static_branch_disable(&virt_spin_lock_key);
}
@@ -473,3 +510,4 @@ struct pv_mmu_ops pv_mmu_ops __ro_after_init = {
EXPORT_SYMBOL (pv_mmu_ops);
EXPORT_SYMBOL_GPL(pv_info);
EXPORT_SYMBOL (pv_irq_ops);
+EXPORT_SYMBOL (pv_spinlock_type);
@@ -81,8 +81,9 @@ void xen_init_lock_cpu(int cpu)
int irq;
char *name;
- if (!xen_pvspin) {
- if (cpu == 0)
+ if (!xen_pvspin ||
+ (pv_spinlock_type & (locktype_queued|locktype_unfair))) {
+ if ((cpu == 0) && !pv_spinlock_type)
static_branch_disable(&virt_spin_lock_key);
return;
}
@@ -109,7 +110,8 @@ void xen_init_lock_cpu(int cpu)
void xen_uninit_lock_cpu(int cpu)
{
- if (!xen_pvspin)
+ if (!xen_pvspin ||
+ (pv_spinlock_type & (locktype_queued|locktype_unfair)))
return;
unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
@@ -130,8 +132,8 @@ void xen_uninit_lock_cpu(int cpu)
*/
void __init xen_init_spinlocks(void)
{
-
- if (!xen_pvspin) {
+ if (!xen_pvspin ||
+ (pv_spinlock_type & (locktype_queued|locktype_unfair))) {
printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
return;
}
Currently, there are 3 different lock types that can be chosen for the x86 architecture: - qspinlock - pvqspinlock - unfair lock One of the above lock types will be chosen at boot time depending on a number of different factors. Ideally, the hypervisors should be able to pick the best performing lock type for the current VM configuration. That is not currently the case as the performance of each lock type are affected by many different factors like the number of vCPUs in the VM, the amount vCPU overcommitment, the CPU type and so on. Generally speaking, unfair lock performs well for VMs with a small number of vCPUs. Native qspinlock may perform better than pvqspinlock if there is vCPU pinning and there is no vCPU over-commitment. This patch adds a new kernel parameter to allow administrator to choose the paravirt spinlock type to be used. VM administrators can experiment with the different lock types and choose one that can best suit their need, if they want to. Hypervisor developers can also use that to experiment with different lock types so that they can come up with a better algorithm to pick the best lock type. The hypervisor paravirt spinlock code will override this new parameter in determining if pvqspinlock should be used. The parameter, however, will override Xen's xen_nopvspin in term of disabling unfair lock. Signed-off-by: Waiman Long <longman@redhat.com> --- Documentation/admin-guide/kernel-parameters.txt | 7 +++++ arch/x86/include/asm/paravirt.h | 9 ++++++ arch/x86/kernel/kvm.c | 3 ++ arch/x86/kernel/paravirt.c | 40 ++++++++++++++++++++++++- arch/x86/xen/spinlock.c | 12 ++++---- 5 files changed, 65 insertions(+), 6 deletions(-)