Hi, Just few nits, patch itself LGTM: On Fri, Jul 9, 2021 at 12:37 AM Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> wrote: > > PV-vcpu-state is a per-CPU struct, which, for the time being, > holds boolean `preempted' vCPU state. During the startup, > given that host supports PV-state, each guest vCPU sends > a pointer to its per-CPU variable to the host as a payload > with the SMCCC HV call, so that host can update vCPU state > when it puts or loads vCPU. > > This has impact on the guest's scheduler: > > [..] > wake_up_process() > try_to_wake_up() > select_task_rq_fair() > available_idle_cpu() > vcpu_is_preempted() > > Some sched benchmarks data is available on the github page [0]. > > [0] https://github.com/sergey-senozhatsky/arm64-vcpu_is_preempted > > Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> > --- > arch/arm64/include/asm/paravirt.h | 19 +++++++ > arch/arm64/kernel/paravirt.c | 94 +++++++++++++++++++++++++++++++ > arch/arm64/kernel/smp.c | 4 ++ > 3 files changed, 117 insertions(+) > > diff --git a/arch/arm64/include/asm/paravirt.h b/arch/arm64/include/asm/paravirt.h > index 9aa193e0e8f2..a3f7665dff38 100644 > --- a/arch/arm64/include/asm/paravirt.h > +++ b/arch/arm64/include/asm/paravirt.h > @@ -2,6 +2,11 @@ > #ifndef _ASM_ARM64_PARAVIRT_H > #define _ASM_ARM64_PARAVIRT_H > > +struct vcpu_state { > + bool preempted; > + u8 reserved[63]; > +}; > + > #ifdef CONFIG_PARAVIRT > #include <linux/static_call_types.h> > > @@ -20,8 +25,22 @@ static inline u64 paravirt_steal_clock(int cpu) > > int __init pv_time_init(void); > > +bool dummy_vcpu_is_preempted(unsigned int cpu); > + > +extern struct static_key pv_vcpu_is_preempted_enabled;. pv_vcpu_is_preempted_enabled static_key is not used in any patch. Maybe it is stale? > +DECLARE_STATIC_CALL(pv_vcpu_is_preempted, dummy_vcpu_is_preempted); > + > +static inline bool paravirt_vcpu_is_preempted(unsigned int cpu) > +{ > + return static_call(pv_vcpu_is_preempted)(cpu); > +} > + > +int __init pv_vcpu_state_init(void); > + > #else > > +#define pv_vcpu_state_init() do {} while (0) > + > #define pv_time_init() do {} while (0) > > #endif // CONFIG_PARAVIRT > diff --git a/arch/arm64/kernel/paravirt.c b/arch/arm64/kernel/paravirt.c > index 75fed4460407..d8fc46795d94 100644 > --- a/arch/arm64/kernel/paravirt.c > +++ b/arch/arm64/kernel/paravirt.c > @@ -40,6 +40,11 @@ struct pv_time_stolen_time_region { > > static DEFINE_PER_CPU(struct pv_time_stolen_time_region, stolen_time_region); > > +static DEFINE_PER_CPU(struct vcpu_state, vcpus_states); > +struct static_key pv_vcpu_is_preempted_enabled; > + > +DEFINE_STATIC_CALL(pv_vcpu_is_preempted, dummy_vcpu_is_preempted); Could we use DEFINE_STATIC_CALL_NULL and get rid of the dummy function? I believe that makes the function trampoline as return instruction, till it is updated. > + > static bool steal_acc = true; > static int __init parse_no_stealacc(char *arg) > { > @@ -165,3 +170,92 @@ int __init pv_time_init(void) > > return 0; > } > + > +bool dummy_vcpu_is_preempted(unsigned int cpu) > +{ > + return false; > +} > + > +static bool __vcpu_is_preempted(unsigned int cpu) > +{ > + struct vcpu_state *st; > + > + st = &per_cpu(vcpus_states, cpu); > + return READ_ONCE(st->preempted); I guess you could just do: { return READ_ONCE(per_cpu(vcpus_states, cpu).preempted); } > +} > + > +static bool has_pv_vcpu_state(void) > +{ > + struct arm_smccc_res res; > + > + /* To detect the presence of PV time support we require SMCCC 1.1+ */ > + if (arm_smccc_1_1_get_conduit() == SMCCC_CONDUIT_NONE) > + return false; > + > + arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID, > + ARM_SMCCC_HV_PV_VCPU_STATE_FEATURES, > + &res); > + > + if (res.a0 != SMCCC_RET_SUCCESS) > + return false; > + return true; > +} > + > +static int __pv_vcpu_state_hook(unsigned int cpu, int event) > +{ > + struct arm_smccc_res res; > + struct vcpu_state *st; > + > + st = &per_cpu(vcpus_states, cpu); > + arm_smccc_1_1_invoke(event, virt_to_phys(st), &res); > + if (res.a0 != SMCCC_RET_SUCCESS) > + return -EINVAL; > + return 0; > +} > + > +static int vcpu_state_init(unsigned int cpu) > +{ > + int ret = __pv_vcpu_state_hook(cpu, ARM_SMCCC_HV_PV_VCPU_STATE_INIT); > + > + if (ret) > + pr_warn("Unable to ARM_SMCCC_HV_PV_STATE_INIT\n"); > + return ret; > +} > + > +static int vcpu_state_release(unsigned int cpu) > +{ > + int ret = __pv_vcpu_state_hook(cpu, ARM_SMCCC_HV_PV_VCPU_STATE_RELEASE); > + > + if (ret) > + pr_warn("Unable to ARM_SMCCC_HV_PV_STATE_RELEASE\n"); > + return ret; > +} > + > +static int pv_vcpu_state_register_hooks(void) > +{ > + int ret; > + > + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, > + "hypervisor/arm/pvstate:starting", > + vcpu_state_init, > + vcpu_state_release); > + if (ret < 0) > + pr_warn("Failed to register CPU hooks\n"); > + return 0; > +} > + > +int __init pv_vcpu_state_init(void) > +{ > + int ret; > + > + if (!has_pv_vcpu_state()) > + return 0; > + > + ret = pv_vcpu_state_register_hooks(); > + if (ret) > + return ret; > + > + static_call_update(pv_vcpu_is_preempted, __vcpu_is_preempted); > + static_key_slow_inc(&pv_vcpu_is_preempted_enabled); I think this static key inc is also stale. thanks, -Joel _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
