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

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Date:   Fri, 26 Jul 2019 20:30:55 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     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>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Juergen Gross <jgross@...e.com>
Subject: [patch 07/12] KVM: LAPIC: Mark hrtimer to expire in hard interrupt
 context

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;