Messages in this thread | | | Subject | Re: [PATCH v2 6/6] KVM: arm64: Support the VCPU preemption check | From | Steven Price <> | Date | Thu, 9 Jan 2020 15:09:28 +0000 |
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On 26/12/2019 13:58, Zengruan Ye wrote: > Support the vcpu_is_preempted() functionality under KVM/arm64. This will > enhance lock performance on overcommitted hosts (more runnable VCPUs > than physical CPUs in the system) as doing busy waits for preempted > VCPUs will hurt system performance far worse than early yielding. > > unix benchmark result: > host: kernel 5.5.0-rc1, HiSilicon Kunpeng920, 8 CPUs > guest: kernel 5.5.0-rc1, 16 VCPUs > > test-case | after-patch | before-patch > ----------------------------------------+-------------------+------------------ > Dhrystone 2 using register variables | 334600751.0 lps | 335319028.3 lps > Double-Precision Whetstone | 32856.1 MWIPS | 32849.6 MWIPS > Execl Throughput | 3662.1 lps | 2718.0 lps > File Copy 1024 bufsize 2000 maxblocks | 432906.4 KBps | 158011.8 KBps > File Copy 256 bufsize 500 maxblocks | 116023.0 KBps | 37664.0 KBps > File Copy 4096 bufsize 8000 maxblocks | 1432769.8 KBps | 441108.8 KBps > Pipe Throughput | 6405029.6 lps | 6021457.6 lps > Pipe-based Context Switching | 185872.7 lps | 184255.3 lps > Process Creation | 4025.7 lps | 3706.6 lps > Shell Scripts (1 concurrent) | 6745.6 lpm | 6436.1 lpm > Shell Scripts (8 concurrent) | 998.7 lpm | 931.1 lpm > System Call Overhead | 3913363.1 lps | 3883287.8 lps > ----------------------------------------+-------------------+------------------ > System Benchmarks Index Score | 1835.1 | 1327.6 > > Signed-off-by: Zengruan Ye <yezengruan@huawei.com> > --- > arch/arm64/include/asm/paravirt.h | 3 + > arch/arm64/kernel/paravirt.c | 117 ++++++++++++++++++++++++++++++ > arch/arm64/kernel/setup.c | 2 + > include/linux/cpuhotplug.h | 1 + > 4 files changed, 123 insertions(+) > > diff --git a/arch/arm64/include/asm/paravirt.h b/arch/arm64/include/asm/paravirt.h > index 7b1c81b544bb..ca3a2c7881f3 100644 > --- a/arch/arm64/include/asm/paravirt.h > +++ b/arch/arm64/include/asm/paravirt.h > @@ -29,6 +29,8 @@ static inline u64 paravirt_steal_clock(int cpu) > > int __init pv_time_init(void); > > +int __init pv_lock_init(void); > + > __visible bool __native_vcpu_is_preempted(int cpu); > > static inline bool pv_vcpu_is_preempted(int cpu) > @@ -39,6 +41,7 @@ static inline bool pv_vcpu_is_preempted(int cpu) > #else > > #define pv_time_init() do {} while (0) > +#define pv_lock_init() do {} while (0) > > #endif // CONFIG_PARAVIRT > > diff --git a/arch/arm64/kernel/paravirt.c b/arch/arm64/kernel/paravirt.c > index d8f1ba8c22ce..bd2ad6a17a26 100644 > --- a/arch/arm64/kernel/paravirt.c > +++ b/arch/arm64/kernel/paravirt.c > @@ -22,6 +22,7 @@ > #include <asm/paravirt.h> > #include <asm/pvclock-abi.h> > #include <asm/smp_plat.h> > +#include <asm/pvlock-abi.h> > > struct static_key paravirt_steal_enabled; > struct static_key paravirt_steal_rq_enabled; > @@ -35,6 +36,10 @@ struct pv_time_stolen_time_region { > struct pvclock_vcpu_stolen_time *kaddr; > }; > > +struct pv_lock_state_region { > + struct pvlock_vcpu_state *kaddr; > +}; > + > static DEFINE_PER_CPU(struct pv_time_stolen_time_region, stolen_time_region); > > static bool steal_acc = true; > @@ -158,3 +163,115 @@ int __init pv_time_init(void) > > return 0; > } > + > +static DEFINE_PER_CPU(struct pv_lock_state_region, lock_state_region); > + > +static bool kvm_vcpu_is_preempted(int cpu) > +{ > + struct pv_lock_state_region *reg; > + __le64 preempted_le; > + > + reg = per_cpu_ptr(&lock_state_region, cpu); > + if (!reg->kaddr) { > + pr_warn_once("PV lock enabled but not configured for cpu %d\n", > + cpu); > + return false; > + } > + > + preempted_le = le64_to_cpu(READ_ONCE(reg->kaddr->preempted)); > + > + return !!(preempted_le & 1);
According to the documentation preempted != 0 means preempted, but here you are checking the LSB. You need to be consistent about the ABI.
> +} > + > +static int pvlock_vcpu_state_dying_cpu(unsigned int cpu) > +{ > + struct pv_lock_state_region *reg; > + > + reg = this_cpu_ptr(&lock_state_region); > + if (!reg->kaddr) > + return 0; > + > + memunmap(reg->kaddr); > + memset(reg, 0, sizeof(*reg)); > + > + return 0; > +} > + > +static int init_pvlock_vcpu_state(unsigned int cpu) > +{ > + struct pv_lock_state_region *reg; > + struct arm_smccc_res res; > + > + reg = this_cpu_ptr(&lock_state_region); > + > + arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_LOCK_PREEMPTED, &res); > + > + if (res.a0 == SMCCC_RET_NOT_SUPPORTED) { > + pr_warn("Failed to init PV lock data structure\n"); > + return -EINVAL; > + } > + > + reg->kaddr = memremap(res.a0, > + sizeof(struct pvlock_vcpu_state), > + MEMREMAP_WB); > + > + if (!reg->kaddr) { > + pr_warn("Failed to map PV lock data structure\n"); > + return -ENOMEM; > + } > + > + return 0; > +} > + > +static int kvm_arm_init_pvlock(void) > +{ > + int ret; > + > + ret = cpuhp_setup_state(CPUHP_AP_ARM_KVM_PVLOCK_STARTING, > + "hypervisor/arm/pvlock:starting", > + init_pvlock_vcpu_state, > + pvlock_vcpu_state_dying_cpu); > + if (ret < 0) { > + pr_warn("PV-lock init failed\n"); > + return ret; > + } > + > + return 0; > +} > + > +static bool has_kvm_pvlock(void) > +{ > + struct arm_smccc_res res; > + > + /* To detect the presence of PV lock support we require SMCCC 1.1+ */ > + if (psci_ops.smccc_version < SMCCC_VERSION_1_1) > + return false; > + > + arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID, > + ARM_SMCCC_HV_PV_LOCK_FEATURES, &res);
As mentioned previously we could do with something more robust to check that the hypervisor is actually KVM before assuming that vendor specific IDs are valid.
Steve
> + > + if (res.a0 != SMCCC_RET_SUCCESS) > + return false; > + > + return true; > +} > + > +int __init pv_lock_init(void) > +{ > + int ret; > + > + if (is_hyp_mode_available()) > + return 0; > + > + if (!has_kvm_pvlock()) > + return 0; > + > + ret = kvm_arm_init_pvlock(); > + if (ret) > + return ret; > + > + pv_ops.lock.vcpu_is_preempted = kvm_vcpu_is_preempted; > + pr_info("using PV-lock preempted\n"); > + > + return 0; > +} > diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c > index 56f664561754..aa3a8b9e710f 100644 > --- a/arch/arm64/kernel/setup.c > +++ b/arch/arm64/kernel/setup.c > @@ -341,6 +341,8 @@ void __init setup_arch(char **cmdline_p) > smp_init_cpus(); > smp_build_mpidr_hash(); > > + pv_lock_init(); > + > /* Init percpu seeds for random tags after cpus are set up. */ > kasan_init_tags(); > > diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h > index e51ee772b9f5..f72ff95ab63a 100644 > --- a/include/linux/cpuhotplug.h > +++ b/include/linux/cpuhotplug.h > @@ -138,6 +138,7 @@ enum cpuhp_state { > CPUHP_AP_DUMMY_TIMER_STARTING, > CPUHP_AP_ARM_XEN_STARTING, > CPUHP_AP_ARM_KVMPV_STARTING, > + CPUHP_AP_ARM_KVM_PVLOCK_STARTING, > CPUHP_AP_ARM_CORESIGHT_STARTING, > CPUHP_AP_ARM64_ISNDEP_STARTING, > CPUHP_AP_SMPCFD_DYING, >
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