From: Rik van Riel <riel@redhat.com>
To: Marcelo Tosatti <mtosatti@redhat.com>, kvm@vger.kernel.org
Cc: Luiz Capitulino <lcapitulino@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Radim Krcmar <rkrcmar@redhat.com>
Subject: Re: [patch 2/2] KVM: x86: add option to advance tscdeadline hrtimer expiration
Date: Wed, 10 Dec 2014 12:11:57 -0500 [thread overview]
Message-ID: <54887EDD.8010708@redhat.com> (raw)
In-Reply-To: <20141210170617.868978945@redhat.com>
On 12/10/2014 12:06 PM, Marcelo Tosatti wrote:
> For the hrtimer which emulates the tscdeadline timer in the guest,
> add an option to advance expiration, and busy spin on VM-entry waiting
> for the actual expiration time to elapse.
>
> This allows achieving low latencies in cyclictest (or any scenario
> which requires strict timing regarding timer expiration).
>
> Reduces cyclictest avg latency by 50%.
>
> Note: this option requires tuning to find the appropriate value
> for a particular hardware/guest combination. One method is to measure the
> average delay between apic_timer_fn and VM-entry.
> Another method is to start with 1000ns, and increase the value
> in say 500ns increments until avg cyclictest numbers stop decreasing.
It would be good to document how this is used, in the changelog.
next prev parent reply other threads:[~2014-12-10 17:20 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-10 17:06 [patch 0/2] KVM: add option to advance tscdeadline hrtimer expiration (v2) Marcelo Tosatti
2014-12-10 17:06 ` [patch 1/2] KVM: x86: add method to test PIR bitmap vector Marcelo Tosatti
2014-12-10 17:10 ` Rik van Riel
2014-12-10 17:27 ` Marcelo Tosatti
2014-12-10 17:50 ` Rik van Riel
2014-12-10 17:57 ` Marcelo Tosatti
2014-12-10 17:06 ` [patch 2/2] KVM: x86: add option to advance tscdeadline hrtimer expiration Marcelo Tosatti
2014-12-10 17:11 ` Rik van Riel [this message]
2014-12-10 17:10 ` [patch 0/2] KVM: add option to advance tscdeadline hrtimer expiration (v2) Paolo Bonzini
2014-12-10 17:27 ` Marcelo Tosatti
-- strict thread matches above, loose matches on Subject: below --
2014-12-10 20:57 [patch 0/2] KVM: add option to advance tscdeadline hrtimer expiration (v3) Marcelo Tosatti
2014-12-10 20:57 ` [patch 2/2] KVM: x86: add option to advance tscdeadline hrtimer expiration Marcelo Tosatti
2014-12-10 23:37 ` Paolo Bonzini
2014-12-11 3:07 ` Marcelo Tosatti
2014-12-11 18:58 ` Paolo Bonzini
2014-12-11 20:48 ` Andy Lutomirski
2014-12-11 20:58 ` Marcelo Tosatti
2014-12-11 21:07 ` Andy Lutomirski
2014-12-11 21:37 ` Rik van Riel
2014-12-11 21:10 ` Paolo Bonzini
2014-12-11 21:16 ` Andy Lutomirski
2014-12-11 21:27 ` Marcelo Tosatti
2014-12-11 21:29 ` Marcelo Tosatti
2014-12-12 18:35 ` Radim Krcmar
2014-12-10 16:53 [patch 0/2] KVM: " Marcelo.Tosatti
2014-12-10 16:53 ` [patch 2/2] KVM: x86: " Marcelo.Tosatti
2014-12-10 17:08 ` Paolo Bonzini
2014-12-10 17:34 ` Marcelo Tosatti
2014-12-10 17:53 ` Paolo Bonzini
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