linux-kernel - Re: [patch 07/12] KVM: LAPIC: Mark hrtimer to expire in hard interrupt context

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Message-ID: <6fea9141-1391-8466-0cf5-27f193daf5c9@redhat.com>
Date:   Fri, 26 Jul 2019 21:41:34 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Juergen Gross <jgross@...e.com>
Subject: Re: [patch 07/12] KVM: LAPIC: Mark hrtimer to expire in hard
 interrupt context

On 26/07/19 20:30, Thomas Gleixner wrote:
> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 
> On PREEMPT_RT enabled kernels unmarked hrtimers are moved into soft
> interrupt expiry mode by default.
> 
> While that's not a functional requirement for the KVM local APIC timer
> emulation, it's a latency issue which can be avoided by marking the timer
> so hard interrupt context expiry is enforced.
> 
> No functional change.
> 
> [ tglx: Split out from larger combo patch. Add changelog. ]
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: kvm@...r.kernel.org
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/lapic.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2302,7 +2302,7 @@ int kvm_create_lapic(struct kvm_vcpu *vc
>  	apic->vcpu = vcpu;
>  
>  	hrtimer_init(&apic->lapic_timer.timer, CLOCK_MONOTONIC,
> -		     HRTIMER_MODE_ABS);
> +		     HRTIMER_MODE_ABS_HARD);
>  	apic->lapic_timer.timer.function = apic_timer_fn;
>  	if (timer_advance_ns == -1) {
>  		apic->lapic_timer.timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT;
> 
> 

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