From mboxrd@z Thu Jan 1 00:00:00 1970 From: yezengruan Subject: Re: [PATCH 5/5] KVM: arm64: Support the vcpu preemption check Date: Thu, 26 Dec 2019 16:34:38 +0800 Message-ID: References: <20191217135549.3240-1-yezengruan@huawei.com> <20191217135549.3240-6-yezengruan@huawei.com> <20191217144032.GD38811@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20191217144032.GD38811@arm.com> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" To: Steven Price Cc: Mark Rutland , "daniel.lezcano@linaro.org" , "kvm@vger.kernel.org" , "linux-doc@vger.kernel.org" , "maz@kernel.org" , Suzuki Poulose , "linux-kernel@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , James Morse , "julien.thierry.kdev@gmail.com" , Catalin Marinas , "linux@armlinux.org.uk" , "will@kernel.org" , "kvmarm@lists.cs.columbia.edu" , "linux-arm-kernel@lists.infradead.org" List-Id: virtualization@lists.linuxfoundation.org Hi Steve, On 2019/12/17 22:40, Steven Price wrote: > On Tue, Dec 17, 2019 at 01:55:49PM +0000, yezengruan@huawei.com wrote: >> From: Zengruan Ye >> >> 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 >> --- >> arch/arm64/include/asm/paravirt.h | 3 + >> arch/arm64/kernel/paravirt.c | 91 +++++++++++++++++++++++++++++++ >> arch/arm64/kernel/setup.c | 2 + >> include/linux/cpuhotplug.h | 1 + >> 4 files changed, 97 insertions(+) >> >> diff --git a/arch/arm64/include/asm/paravirt.h b/arch/arm64/include/asm/paravirt.h >> index 7b1c81b544bb..a2cd0183bbef 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 kvm_guest_init(void); >> + > > This is a *very* generic name - I suggest something like pv_lock_init() > so it's clear what the function actually does. > >> __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 kvm_guest_init() do {} while (0) >> >> #endif // CONFIG_PARAVIRT >> >> diff --git a/arch/arm64/kernel/paravirt.c b/arch/arm64/kernel/paravirt.c >> index d8f1ba8c22ce..a86dead40473 100644 >> --- a/arch/arm64/kernel/paravirt.c >> +++ b/arch/arm64/kernel/paravirt.c >> @@ -22,6 +22,7 @@ >> #include >> #include >> #include >> +#include >> >> struct static_key paravirt_steal_enabled; >> struct static_key paravirt_steal_rq_enabled; >> @@ -158,3 +159,93 @@ int __init pv_time_init(void) >> >> return 0; >> } >> + >> +DEFINE_PER_CPU(struct pvlock_vcpu_state, pvlock_vcpu_region) __aligned(64); >> +EXPORT_PER_CPU_SYMBOL(pvlock_vcpu_region); >> + >> +static int pvlock_vcpu_state_dying_cpu(unsigned int cpu) >> +{ >> + struct pvlock_vcpu_state *reg; >> + >> + reg = this_cpu_ptr(&pvlock_vcpu_region); >> + if (!reg) >> + return -EFAULT; >> + >> + memset(reg, 0, sizeof(*reg)); > > I might be missing something obvious here - but I don't see the point of > this. The hypervisor might immediately overwrite the structure again. > Indeed you should conside a mechanism for the guest to "unregister" the > region - otherwise you will face issues with the likes of kexec. > > For pv_time the memory is allocated by the hypervisor not the guest to > avoid lifetime issues about kexec. Thanks for pointing it out to me! I'll update the memory allocation mechanism of the PV lock structure to avoid lifetime issues about kexec. > >> + >> + return 0; >> +} >> + >> +static int init_pvlock_vcpu_state(unsigned int cpu) >> +{ >> + struct pvlock_vcpu_state *reg; >> + struct arm_smccc_res res; >> + >> + reg = this_cpu_ptr(&pvlock_vcpu_region); >> + if (!reg) >> + return -EFAULT; >> + >> + /* Pass the memory address to host via hypercall */ >> + arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_LOCK_PREEMPTED, >> + virt_to_phys(reg), &res); >> + >> + return 0; >> +} >> + >> +static bool kvm_vcpu_is_preempted(int cpu) >> +{ >> + struct pvlock_vcpu_state *reg = &per_cpu(pvlock_vcpu_region, cpu); >> + >> + if (reg) >> + return !!(reg->preempted & 1); >> + >> + return false; >> +} >> + >> +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) >> + return ret; >> + >> + pv_ops.lock.vcpu_is_preempted = kvm_vcpu_is_preempted; >> + >> + pr_info("using PV-lock preempted\n"); >> + >> + 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); >> + >> + if (res.a0 != SMCCC_RET_SUCCESS) >> + return false; >> + >> + return true; >> +} >> + >> +int __init kvm_guest_init(void) >> +{ >> + if (is_hyp_mode_available()) >> + return 0; >> + >> + if (!has_kvm_pvlock()) >> + return 0; >> + >> + kvm_arm_init_pvlock(); > > Consider reporting errors from kvm_arm_init_pvlock()? At the moment > it's impossible to tell the difference between pvlock not being > supported and something failing in the setup. Good point, I'll update the code. > > Steve > >> + >> + return 0; >> +} >> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c >> index 56f664561754..64c4d515ba2d 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(); >> >> + kvm_guest_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, >> -- >> 2.19.1 >> >> > > . > Thanks, Zengruan