linux-kernel - Re: [patch 31/66] x86/kvm/kvmclock: Convert to hotplug state machine

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Date:	Mon, 11 Jul 2016 16:41:38 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Anna-Maria Gleixner <anna-maria@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Gleb Natapov <gleb@...nel.org>, kvm@...r.kernel.org
Subject: Re: [patch 31/66] x86/kvm/kvmclock: Convert to hotplug state machine

On 11/07/2016 14:28, Anna-Maria Gleixner wrote:
> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 
> Install the callbacks via the state machine and let the core invoke
> the callbacks on the already online CPUs.
> 
> We assumed that the priority ordering was ment to invoke the online
> callback as the last step. In the original code this also invoked the
> down prepare callback as the last step. With the symmetric state
> machine the down prepare callback is now the first step.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Cc: Gleb Natapov <gleb@...nel.org>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: kvm@...r.kernel.org
> Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
> ---
>  arch/x86/kvm/x86.c         |   35 ++++++++---------------------------
>  include/linux/cpuhotplug.h |    1 +
>  2 files changed, 9 insertions(+), 27 deletions(-)
> 
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5552,9 +5552,10 @@ int kvm_fast_pio_out(struct kvm_vcpu *vc
>  }
>  EXPORT_SYMBOL_GPL(kvm_fast_pio_out);
>  
> -static void tsc_bad(void *info)
> +static int kvmclock_cpu_down_prep(unsigned int cpu)
>  {
>  	__this_cpu_write(cpu_tsc_khz, 0);
> +	return 0;
>  }
>  
>  static void tsc_khz_changed(void *data)
> @@ -5659,35 +5660,18 @@ static struct notifier_block kvmclock_cp
>  	.notifier_call  = kvmclock_cpufreq_notifier
>  };
>  
> -static int kvmclock_cpu_notifier(struct notifier_block *nfb,
> -					unsigned long action, void *hcpu)
> +static int kvmclock_cpu_online(unsigned int cpu)
>  {
> -	unsigned int cpu = (unsigned long)hcpu;
> -
> -	switch (action) {
> -		case CPU_ONLINE:
> -		case CPU_DOWN_FAILED:
> -			tsc_khz_changed(NULL);
> -			break;
> -		case CPU_DOWN_PREPARE:
> -			tsc_bad(NULL);
> -			break;
> -	}
> -	return NOTIFY_OK;
> +	tsc_khz_changed(NULL);
> +	return 0;
>  }
>  
> -static struct notifier_block kvmclock_cpu_notifier_block = {
> -	.notifier_call  = kvmclock_cpu_notifier,
> -	.priority = -INT_MAX
> -};
> -
>  static void kvm_timer_init(void)
>  {
>  	int cpu;
>  
>  	max_tsc_khz = tsc_khz;
>  
> -	cpu_notifier_register_begin();
>  	if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
>  #ifdef CONFIG_CPU_FREQ
>  		struct cpufreq_policy policy;
> @@ -5702,12 +5686,9 @@ static void kvm_timer_init(void)
>  					  CPUFREQ_TRANSITION_NOTIFIER);
>  	}
>  	pr_debug("kvm: max_tsc_khz = %ld\n", max_tsc_khz);
> -	for_each_online_cpu(cpu)
> -		smp_call_function_single(cpu, tsc_khz_changed, NULL, 1);
> -
> -	__register_hotcpu_notifier(&kvmclock_cpu_notifier_block);
> -	cpu_notifier_register_done();
>  
> +	cpuhp_setup_state(CPUHP_AP_X86_KVM_CLK_ONLINE, "AP_X86_KVM_CLK_ONLINE",
> +			  kvmclock_cpu_online, kvmclock_cpu_down_prep);
>  }
>  
>  static DEFINE_PER_CPU(struct kvm_vcpu *, current_vcpu);
> @@ -5896,7 +5877,7 @@ void kvm_arch_exit(void)
>  	if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
>  		cpufreq_unregister_notifier(&kvmclock_cpufreq_notifier_block,
>  					    CPUFREQ_TRANSITION_NOTIFIER);
> -	unregister_hotcpu_notifier(&kvmclock_cpu_notifier_block);
> +	cpuhp_remove_state_nocalls(CPUHP_X86_KVM_CLK_ONLINE);
>  #ifdef CONFIG_X86_64
>  	pvclock_gtod_unregister_notifier(&pvclock_gtod_notifier);
>  #endif
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -56,6 +56,7 @@ enum cpuhp_state {
>  	CPUHP_AP_ONLINE_DYN,
>  	CPUHP_AP_ONLINE_DYN_END		= CPUHP_AP_ONLINE_DYN + 30,
>  	CPUHP_AP_X86_HPET_ONLINE,
> +	CPUHP_AP_X86_KVM_CLK_ONLINE,
>  	CPUHP_AP_ACTIVE,
>  	CPUHP_ONLINE,
>  };
> 
> 
> 

Acked-by: Paolo Bonzini <pbonzini@...hat.com>

(I don't have problems with patches sent as attachments, but others might).