From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E8589C2D0C8 for ; Tue, 17 Dec 2019 14:40:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BF31424655 for ; Tue, 17 Dec 2019 14:40:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728576AbfLQOki (ORCPT ); Tue, 17 Dec 2019 09:40:38 -0500 Received: from foss.arm.com ([217.140.110.172]:39214 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728532AbfLQOki (ORCPT ); Tue, 17 Dec 2019 09:40:38 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 474501FB; Tue, 17 Dec 2019 06:40:37 -0800 (PST) Received: from arm.com (e112269-lin.cambridge.arm.com [10.1.196.56]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4B9183F67D; Tue, 17 Dec 2019 06:40:35 -0800 (PST) Date: Tue, 17 Dec 2019 14:40:33 +0000 From: Steven Price To: "yezengruan@huawei.com" Cc: "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.cs.columbia.edu" , "kvm@vger.kernel.org" , "linux-doc@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "maz@kernel.org" , James Morse , "linux@armlinux.org.uk" , Suzuki Poulose , "julien.thierry.kdev@gmail.com" , Catalin Marinas , Mark Rutland , "will@kernel.org" , "daniel.lezcano@linaro.org" Subject: Re: [PATCH 5/5] KVM: arm64: Support the vcpu preemption check Message-ID: <20191217144032.GD38811@arm.com> References: <20191217135549.3240-1-yezengruan@huawei.com> <20191217135549.3240-6-yezengruan@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191217135549.3240-6-yezengruan@huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org 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. > + > + 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. 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 > >