Re: [PATCH v3] cpuidle-haltpoll: vcpu hotplug support

[Marcelo Tosatti <mtosatti@redhat.com>]

On Mon, Sep 02, 2019 at 10:34:07PM +0200, Rafael J. Wysocki wrote:
> On Mon, Sep 2, 2019 at 12:43 PM Joao Martins <joao.m.martins@oracle.com> wrote:
> >
> > When cpus != maxcpus cpuidle-haltpoll will fail to register all vcpus
> > past the online ones and thus fail to register the idle driver.
> > This is because cpuidle_add_sysfs() will return with -ENODEV as a
> > consequence from get_cpu_device() return no device for a non-existing
> > CPU.
> >
> > Instead switch to cpuidle_register_driver() and manually register each
> > of the present cpus through cpuhp_setup_state() callbacks and future
> > ones that get onlined or offlined. This mimmics similar logic that
> > intel_idle does.
> >
> > Fixes: fa86ee90eb11 ("add cpuidle-haltpoll driver")
> > Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> > Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> > ---
> > v3:
> > * register the teardown callback for correct handling of hotunplug
> > and error cases. In case cpuhp_setup_state calls fails (e.g. in one of
> > the cpus that it invoked the callback) it will then call the teardown of
> > the previously enabled devices; so no need to handle that manually in
> > haltpoll_uninit().
> > * use the cpuhp_setup_state() returned dyn allocated state when it
> > succeeds. And use that state in haltpoll_unint() to call
> > cpuhp_remove_state() instead of looping online cpus manually. This
> > is because cpuhp_remove_state() invokes the teardown/offline callback.
> > * fix subsystem name to 'cpuidle' instead of 'idle' in cpuhp_setup_state()
> 
> Marcelo, is the R-by still applicable?
> 
> Paolo, any comments?
> 
> >
> > v2:
> > * move cpus_read_unlock() after unregistering all cpuidle_devices;
> > (Marcello Tosatti)
> > * redundant usage of cpuidle_unregister() when only
> > cpuidle_unregister_driver() suffices; (Marcelo Tosatti)
> > * cpuhp_setup_state() returns a state (> 0) for CPUHP_AP_ONLINE_DYN
> > ---
> >  arch/x86/include/asm/cpuidle_haltpoll.h |  4 +-
> >  arch/x86/kernel/kvm.c                   | 18 +++----
> >  drivers/cpuidle/cpuidle-haltpoll.c      | 68 +++++++++++++++++++++++--
> >  include/linux/cpuidle_haltpoll.h        |  4 +-
> >  4 files changed, 73 insertions(+), 21 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/cpuidle_haltpoll.h b/arch/x86/include/asm/cpuidle_haltpoll.h
> > index ff8607d81526..c8b39c6716ff 100644
> > --- a/arch/x86/include/asm/cpuidle_haltpoll.h
> > +++ b/arch/x86/include/asm/cpuidle_haltpoll.h
> > @@ -2,7 +2,7 @@
> >  #ifndef _ARCH_HALTPOLL_H
> >  #define _ARCH_HALTPOLL_H
> >
> > -void arch_haltpoll_enable(void);
> > -void arch_haltpoll_disable(void);
> > +void arch_haltpoll_enable(unsigned int cpu);
> > +void arch_haltpoll_disable(unsigned int cpu);
> >
> >  #endif
> > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > index 8d150e3732d9..a9b6c4e2446d 100644
> > --- a/arch/x86/kernel/kvm.c
> > +++ b/arch/x86/kernel/kvm.c
> > @@ -880,32 +880,26 @@ static void kvm_enable_host_haltpoll(void *i)
> >         wrmsrl(MSR_KVM_POLL_CONTROL, 1);
> >  }
> >
> > -void arch_haltpoll_enable(void)
> > +void arch_haltpoll_enable(unsigned int cpu)
> >  {
> >         if (!kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL)) {
> > -               printk(KERN_ERR "kvm: host does not support poll control\n");
> > -               printk(KERN_ERR "kvm: host upgrade recommended\n");
> > +               pr_err_once("kvm: host does not support poll control\n");
> > +               pr_err_once("kvm: host upgrade recommended\n");
> >                 return;
> >         }
> >
> > -       preempt_disable();
> >         /* Enable guest halt poll disables host halt poll */
> > -       kvm_disable_host_haltpoll(NULL);
> > -       smp_call_function(kvm_disable_host_haltpoll, NULL, 1);
> > -       preempt_enable();
> > +       smp_call_function_single(cpu, kvm_disable_host_haltpoll, NULL, 1);
> >  }
> >  EXPORT_SYMBOL_GPL(arch_haltpoll_enable);
> >
> > -void arch_haltpoll_disable(void)
> > +void arch_haltpoll_disable(unsigned int cpu)
> >  {
> >         if (!kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL))
> >                 return;
> >
> > -       preempt_disable();
> >         /* Enable guest halt poll disables host halt poll */
> > -       kvm_enable_host_haltpoll(NULL);
> > -       smp_call_function(kvm_enable_host_haltpoll, NULL, 1);
> > -       preempt_enable();
> > +       smp_call_function_single(cpu, kvm_enable_host_haltpoll, NULL, 1);
> >  }
> >  EXPORT_SYMBOL_GPL(arch_haltpoll_disable);
> >  #endif
> > diff --git a/drivers/cpuidle/cpuidle-haltpoll.c b/drivers/cpuidle/cpuidle-haltpoll.c
> > index 9ac093dcbb01..56d8ab814466 100644
> > --- a/drivers/cpuidle/cpuidle-haltpoll.c
> > +++ b/drivers/cpuidle/cpuidle-haltpoll.c
> > @@ -11,12 +11,16 @@
> >   */
> >
> >  #include <linux/init.h>
> > +#include <linux/cpu.h>
> >  #include <linux/cpuidle.h>
> >  #include <linux/module.h>
> >  #include <linux/sched/idle.h>
> >  #include <linux/kvm_para.h>
> >  #include <linux/cpuidle_haltpoll.h>
> >
> > +static struct cpuidle_device __percpu *haltpoll_cpuidle_devices;
> > +static enum cpuhp_state haltpoll_hp_state;
> > +
> >  static int default_enter_idle(struct cpuidle_device *dev,
> >                               struct cpuidle_driver *drv, int index)
> >  {
> > @@ -46,6 +50,46 @@ static struct cpuidle_driver haltpoll_driver = {
> >         .state_count = 2,
> >  };
> >
> > +static int haltpoll_cpu_online(unsigned int cpu)
> > +{
> > +       struct cpuidle_device *dev;
> > +
> > +       dev = per_cpu_ptr(haltpoll_cpuidle_devices, cpu);
> > +       if (!dev->registered) {
> > +               dev->cpu = cpu;
> > +               if (cpuidle_register_device(dev)) {
> > +                       pr_notice("cpuidle_register_device %d failed!\n", cpu);
> > +                       return -EIO;
> > +               }
> > +               arch_haltpoll_enable(cpu);
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static int haltpoll_cpu_offline(unsigned int cpu)
> > +{
> > +       struct cpuidle_device *dev;
> > +
> > +       dev = per_cpu_ptr(haltpoll_cpuidle_devices, cpu);
> > +       if (dev->registered) {
> > +               arch_haltpoll_disable(cpu);
> > +               cpuidle_unregister_device(dev);
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static void haltpoll_uninit(void)
> > +{
> > +       if (haltpoll_hp_state)
> > +               cpuhp_remove_state(haltpoll_hp_state);
> > +       cpuidle_unregister_driver(&haltpoll_driver);
> > +
> > +       free_percpu(haltpoll_cpuidle_devices);
> > +       haltpoll_cpuidle_devices = NULL;
> > +}
> > +
> >  static int __init haltpoll_init(void)
> >  {
> >         int ret;
> > @@ -56,17 +100,31 @@ static int __init haltpoll_init(void)
> >         if (!kvm_para_available())
> >                 return 0;
> >
> > -       ret = cpuidle_register(&haltpoll_driver, NULL);
> > -       if (ret == 0)
> > -               arch_haltpoll_enable();
> > +       ret = cpuidle_register_driver(drv);
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       haltpoll_cpuidle_devices = alloc_percpu(struct cpuidle_device);
> > +       if (haltpoll_cpuidle_devices == NULL) {
> > +               cpuidle_unregister_driver(drv);
> > +               return -ENOMEM;
> > +       }
> > +
> > +       ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "cpuidle/haltpoll:online",
> > +                               haltpoll_cpu_online, haltpoll_cpu_offline);
> > +       if (ret < 0) {
> > +               haltpoll_uninit();
> > +       } else {
> > +               haltpoll_hp_state = ret;
> > +               ret = 0;
> > +       }
> >
> >         return ret;
> >  }
> >
> >  static void __exit haltpoll_exit(void)
> >  {
> > -       arch_haltpoll_disable();
> > -       cpuidle_unregister(&haltpoll_driver);
> > +       haltpoll_uninit();
> >  }
> >
> >  module_init(haltpoll_init);
> > diff --git a/include/linux/cpuidle_haltpoll.h b/include/linux/cpuidle_haltpoll.h
> > index fe5954c2409e..d50c1e0411a2 100644
> > --- a/include/linux/cpuidle_haltpoll.h
> > +++ b/include/linux/cpuidle_haltpoll.h
> > @@ -5,11 +5,11 @@
> >  #ifdef CONFIG_ARCH_CPUIDLE_HALTPOLL
> >  #include <asm/cpuidle_haltpoll.h>
> >  #else
> > -static inline void arch_haltpoll_enable(void)
> > +static inline void arch_haltpoll_enable(unsigned int cpu)
> >  {
> >  }
> >
> > -static inline void arch_haltpoll_disable(void)
> > +static inline void arch_haltpoll_disable(unsigned int cpu)
> >  {
> >  }
> >  #endif
> > --
> > 2.17.1
> >

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>