linux-kernel - Re: [patch V2 31/67] KVM/x86: Remove superfluous SMP function call

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Date:	Thu, 14 Jul 2016 10:21:31 +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>,
	Thomas Gleixner <tglx@...utronix.de>, rt@...utronix.de,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Radim Krcmar <rkrcmar@...hat.com>, kvm@...r.kernel.org
Subject: Re: [patch V2 31/67] KVM/x86: Remove superfluous SMP function call



On 13/07/2016 19:16, Anna-Maria Gleixner wrote:
> From: Anna-Maria Gleixner <anna-maria@...utronix.de>
> 
> Since the following commit:
> 
>   1cf4f629d9d2 ("cpu/hotplug: Move online calls to hotplugged cpu")
> 
> ... the CPU_ONLINE and CPU_DOWN_PREPARE notifiers are always run on the hot
> plugged CPU, and as of commit:
> 
>   3b9d6da67e11 ("cpu/hotplug: Fix rollback during error-out in __cpu_disable()")
> 
> the CPU_DOWN_FAILED notifier also runs on the hot plugged CPU.  This patch
> converts the SMP functional calls into direct calls.
> 
> smp_function_call_single() executes the function with interrupts
> disabled. This calling convention is not preserved because there
> is no reason to do so.
> 
> Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Radim Krcmar <rkrcmar@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: kvm@...r.kernel.org
> ---
>  arch/x86/kvm/x86.c |    6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5662,15 +5662,13 @@ static struct notifier_block kvmclock_cp
>  static int kvmclock_cpu_notifier(struct notifier_block *nfb,
>  					unsigned long action, void *hcpu)
>  {
> -	unsigned int cpu = (unsigned long)hcpu;
> -
>  	switch (action) {
>  		case CPU_ONLINE:
>  		case CPU_DOWN_FAILED:
> -			smp_call_function_single(cpu, tsc_khz_changed, NULL, 1);
> +			tsc_khz_changed(NULL);
>  			break;
>  		case CPU_DOWN_PREPARE:
> -			smp_call_function_single(cpu, tsc_bad, NULL, 1);
> +			tsc_bad(NULL);
>  			break;
>  	}
>  	return NOTIFY_OK;
> 
> 

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