| Message ID | 1509550367-19255-1-git-send-email-longman@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 01/11/17 16:32, Waiman Long wrote: > 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. Hmm, I'm not sure we need pvlock_type _and_ xen_nopvspin. What do others think? > > 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 | 4 +++ > arch/x86/kernel/paravirt.c | 40 ++++++++++++++++++++++++- > arch/x86/xen/spinlock.c | 6 ++-- > 5 files changed, 62 insertions(+), 4 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index f7df49d..c98d9c7 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -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] > diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h > index 12deec7..941a046 100644 > --- a/arch/x86/include/asm/paravirt.h > +++ b/arch/x86/include/asm/paravirt.h > @@ -690,6 +690,15 @@ static __always_inline bool pv_vcpu_is_preempted(long cpu) > > #endif /* SMP && PARAVIRT_SPINLOCKS */ > > +enum pv_spinlock_type { > + locktype_auto, > + locktype_queued, > + locktype_paravirt, > + locktype_unfair, > +}; > + > +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;" > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 8bb9594..3a5d3ec4 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -646,6 +646,10 @@ void __init kvm_spinlock_init(void) > if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) > return; > > + if ((pv_spinlock_type == locktype_queued) || > + (pv_spinlock_type == 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); > diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c > index 041096b..ca35cd3 100644 > --- a/arch/x86/kernel/paravirt.c > +++ b/arch/x86/kernel/paravirt.c > @@ -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_auto)) > static_branch_disable(&virt_spin_lock_key); Really? I don't think locktype_paravirt should disable the static key. Juergen
On 11/01/2017 11:51 AM, Juergen Gross wrote: > On 01/11/17 16:32, Waiman Long wrote: >> 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. > Hmm, I'm not sure we need pvlock_type _and_ xen_nopvspin. What do others > think? I don't think we need xen_nopvspin, but I don't want to remove that without agreement from the community. >> 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_auto)) >> static_branch_disable(&virt_spin_lock_key); > Really? I don't think locktype_paravirt should disable the static key. With paravirt spinlock, it doesn't matter if the static key is disabled or not. Without CONFIG_PARAVIRT_SPINLOCKS, however, it does degenerate into the native qspinlock. So you are right, I should check for paravirt type as well. Cheers, Longman
On 11/01/2017 12:28 PM, Waiman Long wrote: > On 11/01/2017 11:51 AM, Juergen Gross wrote: >> On 01/11/17 16:32, Waiman Long wrote: >>> 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. >> Hmm, I'm not sure we need pvlock_type _and_ xen_nopvspin. What do others >> think? > I don't think we need xen_nopvspin, but I don't want to remove that > without agreement from the community. I also don't think xen_nopvspin will be needed after pvlock_type is introduced. -boris
On 11/01/2017 03:01 PM, Boris Ostrovsky wrote: > On 11/01/2017 12:28 PM, Waiman Long wrote: >> On 11/01/2017 11:51 AM, Juergen Gross wrote: >>> On 01/11/17 16:32, Waiman Long wrote: >>>> 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. >>> Hmm, I'm not sure we need pvlock_type _and_ xen_nopvspin. What do others >>> think? >> I don't think we need xen_nopvspin, but I don't want to remove that >> without agreement from the community. > I also don't think xen_nopvspin will be needed after pvlock_type is > introduced. > > -boris Another reason that I didn't try to remove xen_nopvspin is backward compatibility concern. One way to handle it is to depreciate it and treat it as an alias to pvlock_type=queued. Cheers, Longman
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index f7df49d..c98d9c7 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -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] diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h index 12deec7..941a046 100644 --- a/arch/x86/include/asm/paravirt.h +++ b/arch/x86/include/asm/paravirt.h @@ -690,6 +690,15 @@ static __always_inline bool pv_vcpu_is_preempted(long cpu) #endif /* SMP && PARAVIRT_SPINLOCKS */ +enum pv_spinlock_type { + locktype_auto, + locktype_queued, + locktype_paravirt, + locktype_unfair, +}; + +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;" diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 8bb9594..3a5d3ec4 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -646,6 +646,10 @@ void __init kvm_spinlock_init(void) if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) return; + if ((pv_spinlock_type == locktype_queued) || + (pv_spinlock_type == 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); diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c index 041096b..ca35cd3 100644 --- a/arch/x86/kernel/paravirt.c +++ b/arch/x86/kernel/paravirt.c @@ -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_auto)) 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); diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c index 1e1462d..9fc8eab 100644 --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -82,7 +82,7 @@ void xen_init_lock_cpu(int cpu) char *name; if (!xen_pvspin) { - if (cpu == 0) + if ((cpu == 0) && (pv_spinlock_type == locktype_auto)) static_branch_disable(&virt_spin_lock_key); return; } @@ -130,8 +130,8 @@ void xen_uninit_lock_cpu(int cpu) */ void __init xen_init_spinlocks(void) { - - if (!xen_pvspin) { + if (!xen_pvspin || (pv_spinlock_type == locktype_queued) || + (pv_spinlock_type == 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 | 4 +++ arch/x86/kernel/paravirt.c | 40 ++++++++++++++++++++++++- arch/x86/xen/spinlock.c | 6 ++-- 5 files changed, 62 insertions(+), 4 deletions(-)