| Message ID | 1518187673-70832-1-git-send-email-wanpengli@tencent.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Feb 09, 2018 at 06:47:52AM -0800, Wanpeng Li wrote: > From: Wanpeng Li <wanpengli@tencent.com> > > Waiman Long mentioned that: > > 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 performance hint to allow hypervisor admin to choose > the qspinlock to be used when a dedicated pCPU is available. > > PV_DEDICATED = 1, PV_UNHALT = anything: default is qspinlock > PV_DEDICATED = 0, PV_UNHALT = 1: default is Hybrid PV queued/unfair lock > PV_DEDICATED = 0, PV_UNHALT = 0: default is tas > > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Cc: Eduardo Habkost <ehabkost@redhat.com> > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > --- > v1 -> v2: > * update to KVM_HINTS_DEDICATED > > Documentation/virtual/kvm/cpuid.txt | 6 ++++++ > arch/x86/include/uapi/asm/kvm_para.h | 2 ++ > arch/x86/kernel/kvm.c | 6 ++++++ > 3 files changed, 14 insertions(+) > > diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt > index 87a7506..d54cc79 100644 > --- a/Documentation/virtual/kvm/cpuid.txt > +++ b/Documentation/virtual/kvm/cpuid.txt > @@ -66,3 +66,9 @@ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side > || || per-cpu warps are expected in > || || kvmclock. > ------------------------------------------------------------------------------ > +KVM_HINTS_DEDICATED || 0 || guest checks this feature bit > + || || to determine if they run on > + || || dedicated vCPUs, allowing opti- > + || || mizations such as usage of > + || || qspinlocks. I assume you don't mean CPUID[0x40000001].EAX[bit 0] here, because it is already used for KVM_FEATURE_CLOCKSOURCE. I guess you will want a separate table for CPUID[0x40000001].EDX bits? > +------------------------------------------------------------------------------ > diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h > index 6cfa9c8..d65b16b 100644 > --- a/arch/x86/include/uapi/asm/kvm_para.h > +++ b/arch/x86/include/uapi/asm/kvm_para.h > @@ -28,6 +28,8 @@ > #define KVM_FEATURE_PV_TLB_FLUSH 9 > #define KVM_FEATURE_ASYNC_PF_VMEXIT 10 > > +#define KVM_HINTS_DEDICATED 0 > + > /* The last 8 bits are used to indicate how to interpret the flags field > * in pvclock structure. If no bits are set, all flags are ignored. > */ > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 971babe..7f4c92d 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -724,6 +724,12 @@ void __init kvm_spinlock_init(void) > { > if (!kvm_para_available()) > return; > + > + if (kvm_para_has_feature(KVM_HINTS_DEDICATED)) { This is checking CPUID{0x40000001].EAX[bit 0] (KVM_FEATURE_CLOCKSOURCE), isn't it? > + static_branch_disable(&virt_spin_lock_key); > + return; > + } > + > /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ > if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) > return; > -- > 2.7.4 >
diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt index 87a7506..d54cc79 100644 --- a/Documentation/virtual/kvm/cpuid.txt +++ b/Documentation/virtual/kvm/cpuid.txt @@ -66,3 +66,9 @@ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side || || per-cpu warps are expected in || || kvmclock. ------------------------------------------------------------------------------ +KVM_HINTS_DEDICATED || 0 || guest checks this feature bit + || || to determine if they run on + || || dedicated vCPUs, allowing opti- + || || mizations such as usage of + || || qspinlocks. +------------------------------------------------------------------------------ diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h index 6cfa9c8..d65b16b 100644 --- a/arch/x86/include/uapi/asm/kvm_para.h +++ b/arch/x86/include/uapi/asm/kvm_para.h @@ -28,6 +28,8 @@ #define KVM_FEATURE_PV_TLB_FLUSH 9 #define KVM_FEATURE_ASYNC_PF_VMEXIT 10 +#define KVM_HINTS_DEDICATED 0 + /* The last 8 bits are used to indicate how to interpret the flags field * in pvclock structure. If no bits are set, all flags are ignored. */ diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 971babe..7f4c92d 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -724,6 +724,12 @@ void __init kvm_spinlock_init(void) { if (!kvm_para_available()) return; + + if (kvm_para_has_feature(KVM_HINTS_DEDICATED)) { + static_branch_disable(&virt_spin_lock_key); + return; + } + /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) return;