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SubjectRe: [PATCH] KVM: LAPIC: Loose fluctuation filter for auto tune lapic_timer_advance_ns
On Thu, 26 Sep 2019 at 03:29, Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
>
> On Wed, Sep 25, 2019 at 01:47:04PM +0800, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@tencent.com>
> >
> > 5000 guest cycles delta is easy to encounter on desktop, per-vCPU
> > lapic_timer_advance_ns always keeps at 1000ns initial value, lets
> > loose fluctuation filter a bit to make auto tune can make some
> > progress.
> >
> > Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> > ---
> > arch/x86/kvm/lapic.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index 3a3a685..258407e 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -67,7 +67,7 @@
> >
> > static bool lapic_timer_advance_dynamic __read_mostly;
> > #define LAPIC_TIMER_ADVANCE_ADJUST_MIN 100
> > -#define LAPIC_TIMER_ADVANCE_ADJUST_MAX 5000
> > +#define LAPIC_TIMER_ADVANCE_ADJUST_MAX 10000
> > #define LAPIC_TIMER_ADVANCE_ADJUST_INIT 1000
> > /* step-by-step approximation to mitigate fluctuation */
> > #define LAPIC_TIMER_ADVANCE_ADJUST_STEP 8
> > @@ -1504,7 +1504,7 @@ static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu,
> > timer_advance_ns += ns/LAPIC_TIMER_ADVANCE_ADJUST_STEP;
> > }
> >
> > - if (unlikely(timer_advance_ns > LAPIC_TIMER_ADVANCE_ADJUST_MAX))
> > + if (unlikely(timer_advance_ns > LAPIC_TIMER_ADVANCE_ADJUST_MAX/2))
>
> Doh, missed that these are two different time domains in the original
> review, i.e. ns vs. cycles.

I try to save one #define in this patch, will fold below in next version.

Wanpeng

>
> We should use separate defines for the filter since that check is done
> in cycles. Not sure what names to use to keep things somewhat clear.
>
> Maybe s/ADJUST/EXPIRE for the cycles, and s/ADJUST/NS for the ns ones?
> E.g.:
>
> #define LAPIC_TIMER_ADVANCE_EXPIRE_MIN 100
> #define LAPIC_TIMER_ADVANCE_EXPIRE_MAX 10000
> #define LAPIC_TIMER_ADVANCE_NS_MAX 5000
> #define LAPIC_TIMER_ADVANCE_NS_INIT 1000
>
> > timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT;
> > apic->lapic_timer.timer_advance_ns = timer_advance_ns;
> > }
> > --
> > 2.7.4
> >

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