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Date: Fri, 6 Oct 2017 17:04:34 +0200 From: Radim Krčmář <rkrcmar@...hat.com> To: Wanpeng Li <kernellwp@...il.com> Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, Wanpeng Li <wanpeng.li@...mail.com> Subject: Re: [PATCH v6 2/3] KVM: LAPIC: Keep timer running when switching between one-shot and periodic mode 2017-10-06 15:17+0200, Radim Krčmář: > 2017-10-05 18:54-0700, Wanpeng Li: > > From: Wanpeng Li <wanpeng.li@...mail.com> > > > > If we take TSC-deadline mode timer out of the picture, the Intel SDM > > does not say that the timer is disable when the timer mode is change, > > either from one-shot to periodic or vice versa. > > > > After this patch, the timer is no longer disarmed on change of mode, so > > the counter (TMCCT) keeps counting down. > > > > So what does a write to LVTT changes ? On baremetal, the change of mode > > is probably taken into account only when the counter reach 0. When this > > happen, LVTT is use to figure out if the counter should restard counting > > down from TMICT (so periodic mode) or stop counting (if one-shot mode). > > > > This patch is based on observation of the behavior of the APIC timer on > > baremetal as well as check that they does not go against the description > > written in the Intel SDM. > > > > Cc: Paolo Bonzini <pbonzini@...hat.com> > > Cc: Radim Krčmář <rkrcmar@...hat.com> > > Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com> > > --- > > arch/x86/kvm/lapic.c | 8 ++++++-- > > 1 file changed, 6 insertions(+), 2 deletions(-) > > Queued the first two patches, thanks. > > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > > index 8841bb5..14f63b3 100644 > > --- a/arch/x86/kvm/lapic.c > > +++ b/arch/x86/kvm/lapic.c > > @@ -1329,10 +1329,14 @@ static void apic_update_lvtt(struct kvm_lapic *apic) > > > > if (apic->lapic_timer.timer_mode != timer_mode) { > > if (apic_lvtt_tscdeadline(apic) != (timer_mode == > > - APIC_LVT_TIMER_TSCDEADLINE)) > > + APIC_LVT_TIMER_TSCDEADLINE)) { > > kvm_lapic_set_reg(apic, APIC_TMICT, 0); > > + hrtimer_cancel(&apic->lapic_timer.timer); > > + } > > + if (apic_lvtt_oneshot(apic) && (timer_mode == > > + APIC_LVT_TIMER_PERIODIC)) > > + limit_periodic_timer_frequency(apic); I noticed a problem here that required slight changes (the current code never actually did the rate limiting), please see kvm/queue. > > apic->lapic_timer.timer_mode = timer_mode; > > - hrtimer_cancel(&apic->lapic_timer.timer); > > } > > } > > > > -- > > 2.7.4 > >
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