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Date: Sat, 11 Jan 2020 15:33:16 +0800
From: yezengruan <yezengruan@...wei.com>
To: Steven Price <steven.price@....com>,
<linux-kernel@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>,
<kvmarm@...ts.cs.columbia.edu>, <kvm@...r.kernel.org>,
<linux-doc@...r.kernel.org>,
<virtualization@...ts.linux-foundation.org>
CC: <maz@...nel.org>, <james.morse@....com>, <linux@...linux.org.uk>,
<suzuki.poulose@....com>, <julien.thierry.kdev@...il.com>,
<catalin.marinas@....com>, <mark.rutland@....com>,
<will@...nel.org>, <daniel.lezcano@...aro.org>,
"Wanghaibin (D)" <wanghaibin.wang@...wei.com>
Subject: Re: [PATCH v2 6/6] KVM: arm64: Support the VCPU preemption check
Hi Steve,
On 2020/1/9 23:09, Steven Price wrote:
> 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@...wei.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.
Thanks for posting this. I'll update the code.
>
>> +}
>> +
>> +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.
Will update next version.
>
> 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,
>>
>
>
> .
Thanks,
Zengruan
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