linux-kernel - Re: [PATCH] KVM: LAPIC: Periodically revaluate appropriate lapic_timer_advance

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Message-ID: <CANRm+CwMMUEyZXmiUu5Y8GA=BEUYGLw31CRyZTc2uA+ct4Bamg@mail.gmail.com>
Date:   Mon, 12 Aug 2019 17:06:15 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH] KVM: LAPIC: Periodically revaluate appropriate lapic_timer_advance_ns

On Fri, 9 Aug 2019 at 18:24, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 09/08/19 07:45, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.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.

Regards,
Wanpeng Li