| Message ID | 1571102367-31595-4-git-send-email-zhenzhong.duan@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add a unified parameter "nopvspin" | expand |
Hi vitaly This patch is based on your suggestion on v5, appreciate your further review:) Thanks Zhenzhong On 2019/10/15 9:19, Zhenzhong Duan wrote: > There are cases where a guest tries to switch spinlocks to bare metal > behavior (e.g. by setting "xen_nopvspin" on XEN platform and > "hv_nopvspin" on HYPER_V). > > That feature is missed on KVM, add a new parameter "nopvspin" to disable > PV spinlocks for KVM guest. > > The new 'nopvspin' parameter will also replace Xen and Hyper-V specific > parameters in future patches. > > Define variable nopvsin as global because it will be used in future > patches as above. > > Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Borislav Petkov <bp@alien8.de> > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krcmar <rkrcmar@redhat.com> > Cc: Sean Christopherson <sean.j.christopherson@intel.com> > Cc: Vitaly Kuznetsov <vkuznets@redhat.com> > Cc: Wanpeng Li <wanpengli@tencent.com> > Cc: Jim Mattson <jmattson@google.com> > Cc: Joerg Roedel <joro@8bytes.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Will Deacon <will@kernel.org> > --- > Documentation/admin-guide/kernel-parameters.txt | 5 ++++ > arch/x86/include/asm/qspinlock.h | 1 + > arch/x86/kernel/kvm.c | 34 ++++++++++++++++++++++--- > kernel/locking/qspinlock.c | 7 +++++ > 4 files changed, 43 insertions(+), 4 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index a84a83f..bd49ed2 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -5334,6 +5334,11 @@ > as generic guest with no PV drivers. Currently support > XEN HVM, KVM, HYPER_V and VMWARE guest. > > + nopvspin [X86,KVM] > + Disables the qspinlock slow path using PV optimizations > + which allow the hypervisor to 'idle' the guest on lock > + contention. > + > xirc2ps_cs= [NET,PCMCIA] > Format: > <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] > diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h > index 444d6fd..d86ab94 100644 > --- a/arch/x86/include/asm/qspinlock.h > +++ b/arch/x86/include/asm/qspinlock.h > @@ -32,6 +32,7 @@ static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lo > extern void __pv_init_lock_hash(void); > extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); > extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock *lock); > +extern bool nopvspin; > > #define queued_spin_unlock queued_spin_unlock > /** > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 249f14a..e9c76d8 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -825,18 +825,44 @@ __visible bool __kvm_vcpu_is_preempted(long cpu) > */ > void __init kvm_spinlock_init(void) > { > - /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ > - if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) > + /* > + * PV spinlocks is disabled if no host side support, then native > + * qspinlock will be used. As native qspinlock is a fair lock, there is > + * lock holder preemption issue using it in a guest, imaging one pCPU > + * running 10 vCPUs of same guest contending same lock. > + * > + * virt_spin_lock() is introduced as an optimization for that scenario > + * which is enabled by virt_spin_lock_key key. To use that optimization, > + * virt_spin_lock_key isn't disabled here. > + */ > + if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) { > + pr_info("PV spinlocks disabled, no host support.\n"); > return; > + } > > + /* > + * Disable PV qspinlock and use native qspinlock when dedicated pCPUs > + * are available. > + */ > if (kvm_para_has_hint(KVM_HINTS_REALTIME)) { > + pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME hints.\n"); > + static_branch_disable(&virt_spin_lock_key); > + return; > + } > + > + if (num_possible_cpus() == 1) { > + pr_info("PV spinlocks disabled, single CPU.\n"); > static_branch_disable(&virt_spin_lock_key); > return; > } > > - /* Don't use the pvqspinlock code if there is only 1 vCPU. */ > - if (num_possible_cpus() == 1) > + if (nopvspin) { > + pr_info("PV spinlocks disabled, forced by \"nopvspin\" parameter.\n"); > + static_branch_disable(&virt_spin_lock_key); > return; > + } > + > + pr_info("PV spinlocks enabled\n"); > > __pv_init_lock_hash(); > pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; > diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c > index 2473f10..75193d6 100644 > --- a/kernel/locking/qspinlock.c > +++ b/kernel/locking/qspinlock.c > @@ -580,4 +580,11 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) > #include "qspinlock_paravirt.h" > #include "qspinlock.c" > > +bool nopvspin __initdata; > +static __init int parse_nopvspin(char *arg) > +{ > + nopvspin = true; > + return 0; > +} > +early_param("nopvspin", parse_nopvspin); > #endif
Zhenzhong Duan <zhenzhong.duan@oracle.com> writes: > There are cases where a guest tries to switch spinlocks to bare metal > behavior (e.g. by setting "xen_nopvspin" on XEN platform and > "hv_nopvspin" on HYPER_V). > > That feature is missed on KVM, add a new parameter "nopvspin" to disable > PV spinlocks for KVM guest. > > The new 'nopvspin' parameter will also replace Xen and Hyper-V specific > parameters in future patches. > > Define variable nopvsin as global because it will be used in future > patches as above. > > Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Borislav Petkov <bp@alien8.de> > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krcmar <rkrcmar@redhat.com> > Cc: Sean Christopherson <sean.j.christopherson@intel.com> > Cc: Vitaly Kuznetsov <vkuznets@redhat.com> > Cc: Wanpeng Li <wanpengli@tencent.com> > Cc: Jim Mattson <jmattson@google.com> > Cc: Joerg Roedel <joro@8bytes.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Will Deacon <will@kernel.org> > --- > Documentation/admin-guide/kernel-parameters.txt | 5 ++++ > arch/x86/include/asm/qspinlock.h | 1 + > arch/x86/kernel/kvm.c | 34 ++++++++++++++++++++++--- > kernel/locking/qspinlock.c | 7 +++++ > 4 files changed, 43 insertions(+), 4 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index a84a83f..bd49ed2 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -5334,6 +5334,11 @@ > as generic guest with no PV drivers. Currently support > XEN HVM, KVM, HYPER_V and VMWARE guest. > > + nopvspin [X86,KVM] > + Disables the qspinlock slow path using PV optimizations > + which allow the hypervisor to 'idle' the guest on lock > + contention. > + > xirc2ps_cs= [NET,PCMCIA] > Format: > <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] > diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h > index 444d6fd..d86ab94 100644 > --- a/arch/x86/include/asm/qspinlock.h > +++ b/arch/x86/include/asm/qspinlock.h > @@ -32,6 +32,7 @@ static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lo > extern void __pv_init_lock_hash(void); > extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); > extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock *lock); > +extern bool nopvspin; > > #define queued_spin_unlock queued_spin_unlock > /** > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 249f14a..e9c76d8 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -825,18 +825,44 @@ __visible bool __kvm_vcpu_is_preempted(long cpu) > */ > void __init kvm_spinlock_init(void) > { > - /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ > - if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) > + /* > + * PV spinlocks is disabled if no host side support, then native > + * qspinlock will be used. As native qspinlock is a fair lock, there is > + * lock holder preemption issue using it in a guest, imaging one pCPU > + * running 10 vCPUs of same guest contending same lock. > + * > + * virt_spin_lock() is introduced as an optimization for that scenario > + * which is enabled by virt_spin_lock_key key. To use that optimization, > + * virt_spin_lock_key isn't disabled here. > + */ My take (if I properly understood what you say) would be: "In case host doesn't support KVM_FEATURE_PV_UNHALT there is still an advantage of keeping virt_spin_lock_key enabled: virt_spin_lock() is preferred over native qspinlock when vCPU is preempted." > + if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) { > + pr_info("PV spinlocks disabled, no host support.\n"); > return; > + } > > + /* > + * Disable PV qspinlock and use native qspinlock when dedicated pCPUs > + * are available. > + */ > if (kvm_para_has_hint(KVM_HINTS_REALTIME)) { > + pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME hints.\n"); > + static_branch_disable(&virt_spin_lock_key); > + return; > + } > + > + if (num_possible_cpus() == 1) { > + pr_info("PV spinlocks disabled, single CPU.\n"); > static_branch_disable(&virt_spin_lock_key); > return; > } > > - /* Don't use the pvqspinlock code if there is only 1 vCPU. */ > - if (num_possible_cpus() == 1) > + if (nopvspin) { > + pr_info("PV spinlocks disabled, forced by \"nopvspin\" parameter.\n"); > + static_branch_disable(&virt_spin_lock_key); > return; You could've replaced this 'static_branch_disable(); return;' pattern with a goto to the end of the function to save a few lines but this looks good anyways. Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com> > + } > + > + pr_info("PV spinlocks enabled\n"); > > __pv_init_lock_hash(); > pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; > diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c > index 2473f10..75193d6 100644 > --- a/kernel/locking/qspinlock.c > +++ b/kernel/locking/qspinlock.c > @@ -580,4 +580,11 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) > #include "qspinlock_paravirt.h" > #include "qspinlock.c" > > +bool nopvspin __initdata; > +static __init int parse_nopvspin(char *arg) > +{ > + nopvspin = true; > + return 0; > +} > +early_param("nopvspin", parse_nopvspin); > #endif
On 2019/10/21 19:14, Vitaly Kuznetsov wrote: >> index 249f14a..e9c76d8 100644 >> --- a/arch/x86/kernel/kvm.c >> +++ b/arch/x86/kernel/kvm.c >> @@ -825,18 +825,44 @@ __visible bool __kvm_vcpu_is_preempted(long cpu) >> */ >> void __init kvm_spinlock_init(void) >> { >> - /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ >> - if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) >> + /* >> + * PV spinlocks is disabled if no host side support, then native >> + * qspinlock will be used. As native qspinlock is a fair lock, there is >> + * lock holder preemption issue using it in a guest, imaging one pCPU >> + * running 10 vCPUs of same guest contending same lock. >> + * >> + * virt_spin_lock() is introduced as an optimization for that scenario >> + * which is enabled by virt_spin_lock_key key. To use that optimization, >> + * virt_spin_lock_key isn't disabled here. >> + */ > My take (if I properly understood what you say) would be: > > "In case host doesn't support KVM_FEATURE_PV_UNHALT there is still an > advantage of keeping virt_spin_lock_key enabled: virt_spin_lock() is > preferred over native qspinlock when vCPU is preempted." Yes, that's what I mean, maybe I didn't explain clearly due to my pool english, I'll use your explanation instead. > >> + if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) { >> + pr_info("PV spinlocks disabled, no host support.\n"); >> return; >> + } >> >> + /* >> + * Disable PV qspinlock and use native qspinlock when dedicated pCPUs >> + * are available. >> + */ >> if (kvm_para_has_hint(KVM_HINTS_REALTIME)) { >> + pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME hints.\n"); >> + static_branch_disable(&virt_spin_lock_key); >> + return; >> + } >> + >> + if (num_possible_cpus() == 1) { >> + pr_info("PV spinlocks disabled, single CPU.\n"); >> static_branch_disable(&virt_spin_lock_key); >> return; >> } >> >> - /* Don't use the pvqspinlock code if there is only 1 vCPU. */ >> - if (num_possible_cpus() == 1) >> + if (nopvspin) { >> + pr_info("PV spinlocks disabled, forced by \"nopvspin\" parameter.\n"); >> + static_branch_disable(&virt_spin_lock_key); >> return; > You could've replaced this 'static_branch_disable(); return;' pattern > with a goto to the end of the function to save a few lines but this > looks good anyways. > > Reviewed-by: Vitaly Kuznetsov<vkuznets@redhat.com> Ok, will do, thanks for review. Zhenzhong
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index a84a83f..bd49ed2 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5334,6 +5334,11 @@ as generic guest with no PV drivers. Currently support XEN HVM, KVM, HYPER_V and VMWARE guest. + nopvspin [X86,KVM] + Disables the qspinlock slow path using PV optimizations + which allow the hypervisor to 'idle' the guest on lock + contention. + xirc2ps_cs= [NET,PCMCIA] Format: <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h index 444d6fd..d86ab94 100644 --- a/arch/x86/include/asm/qspinlock.h +++ b/arch/x86/include/asm/qspinlock.h @@ -32,6 +32,7 @@ static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lo extern void __pv_init_lock_hash(void); extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock *lock); +extern bool nopvspin; #define queued_spin_unlock queued_spin_unlock /** diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 249f14a..e9c76d8 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -825,18 +825,44 @@ __visible bool __kvm_vcpu_is_preempted(long cpu) */ void __init kvm_spinlock_init(void) { - /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ - if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) + /* + * PV spinlocks is disabled if no host side support, then native + * qspinlock will be used. As native qspinlock is a fair lock, there is + * lock holder preemption issue using it in a guest, imaging one pCPU + * running 10 vCPUs of same guest contending same lock. + * + * virt_spin_lock() is introduced as an optimization for that scenario + * which is enabled by virt_spin_lock_key key. To use that optimization, + * virt_spin_lock_key isn't disabled here. + */ + if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) { + pr_info("PV spinlocks disabled, no host support.\n"); return; + } + /* + * Disable PV qspinlock and use native qspinlock when dedicated pCPUs + * are available. + */ if (kvm_para_has_hint(KVM_HINTS_REALTIME)) { + pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME hints.\n"); + static_branch_disable(&virt_spin_lock_key); + return; + } + + if (num_possible_cpus() == 1) { + pr_info("PV spinlocks disabled, single CPU.\n"); static_branch_disable(&virt_spin_lock_key); return; } - /* Don't use the pvqspinlock code if there is only 1 vCPU. */ - if (num_possible_cpus() == 1) + if (nopvspin) { + pr_info("PV spinlocks disabled, forced by \"nopvspin\" parameter.\n"); + static_branch_disable(&virt_spin_lock_key); return; + } + + pr_info("PV spinlocks enabled\n"); __pv_init_lock_hash(); pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 2473f10..75193d6 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -580,4 +580,11 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) #include "qspinlock_paravirt.h" #include "qspinlock.c" +bool nopvspin __initdata; +static __init int parse_nopvspin(char *arg) +{ + nopvspin = true; + return 0; +} +early_param("nopvspin", parse_nopvspin); #endif
There are cases where a guest tries to switch spinlocks to bare metal behavior (e.g. by setting "xen_nopvspin" on XEN platform and "hv_nopvspin" on HYPER_V). That feature is missed on KVM, add a new parameter "nopvspin" to disable PV spinlocks for KVM guest. The new 'nopvspin' parameter will also replace Xen and Hyper-V specific parameters in future patches. Define variable nopvsin as global because it will be used in future patches as above. Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Radim Krcmar <rkrcmar@redhat.com> Cc: Sean Christopherson <sean.j.christopherson@intel.com> Cc: Vitaly Kuznetsov <vkuznets@redhat.com> Cc: Wanpeng Li <wanpengli@tencent.com> Cc: Jim Mattson <jmattson@google.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will@kernel.org> --- Documentation/admin-guide/kernel-parameters.txt | 5 ++++ arch/x86/include/asm/qspinlock.h | 1 + arch/x86/kernel/kvm.c | 34 ++++++++++++++++++++++--- kernel/locking/qspinlock.c | 7 +++++ 4 files changed, 43 insertions(+), 4 deletions(-)