From: Wanpeng Li <kernellwp@gmail.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
"Radim Krčmář" <rkrcmar@redhat.com>
Subject: Re: [PATCH] KVM: LAPIC: Periodically revaluate appropriate lapic_timer_advance_ns
Date: Thu, 15 Aug 2019 12:04:48 +0800 [thread overview]
Message-ID: <CANRm+CzGNyST4=BtE-eKvjB-PUVVoM-gUC2Np8NH7tm0Gp2_nQ@mail.gmail.com> (raw)
In-Reply-To: <ba07fb02-9b55-15e4-d240-24da59e09369@redhat.com>
On Wed, 14 Aug 2019 at 20:50, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 12/08/19 11:06, Wanpeng Li wrote:
> > On Fri, 9 Aug 2019 at 18:24, Paolo Bonzini <pbonzini@redhat.com> wrote:
> >>
> >> On 09/08/19 07:45, Wanpeng Li wrote:
> >>> From: Wanpeng Li <wanpengli@tencent.com>
> >>>
> >>> Even if for realtime CPUs, cache line bounces, frequency scaling, presence
> >>> of higher-priority RT tasks, etc can cause different response. These
> >>> interferences should be considered and periodically revaluate whether
> >>> or not the lapic_timer_advance_ns value is the best, do nothing if it is,
> >>> otherwise recaluate again.
> >>
> >> How much fluctuation do you observe between different runs?
> >
> > Sometimes can ~1000 cycles after converting to guest tsc freq.
>
> Hmm, I wonder if we need some kind of continuous smoothing. Something like
Actually this can fluctuate drastically instead of continuous
smoothing during testing (running linux guest instead of
kvm-unit-tests).
>
> if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE) {
> /* no update for random fluctuations */
> return;
> }
>
> if (unlikely(timer_advance_ns > 5000))
> timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT;
> apic->lapic_timer.timer_advance_ns = timer_advance_ns;
>
> and removing all the timer_advance_adjust_done stuff. What do you think?
I just sent out v2, periodically revaluate and get a minimal
conservative value from these revaluate points. Please have a look. :)
Regards,
Wanpeng Li
prev parent reply other threads:[~2019-08-15 4:05 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-09 5:45 [PATCH] KVM: LAPIC: Periodically revaluate appropriate lapic_timer_advance_ns Wanpeng Li
2019-08-09 10:24 ` Paolo Bonzini
2019-08-12 9:06 ` Wanpeng Li
2019-08-14 12:50 ` Paolo Bonzini
2019-08-15 4:04 ` Wanpeng Li [this message]
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