From: Paolo Bonzini <pbonzini@redhat.com>
To: Wanpeng Li <kernellwp@gmail.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: Wed, 14 Aug 2019 14:50:01 +0200 [thread overview]
Message-ID: <ba07fb02-9b55-15e4-d240-24da59e09369@redhat.com> (raw)
In-Reply-To: <CANRm+CwMMUEyZXmiUu5Y8GA=BEUYGLw31CRyZTc2uA+ct4Bamg@mail.gmail.com>
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
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?
Paolo
next prev parent reply other threads:[~2019-08-14 12:50 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 [this message]
2019-08-15 4:04 ` Wanpeng Li
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