From: Marcelo Tosatti <mtosatti@redhat.com>
To: Gleb Natapov <gleb@redhat.com>
Cc: kvm-devel <kvm@vger.kernel.org>, Glauber Costa <glommer@gmail.com>
Subject: Re: KVM: x86: limit difference between kvmclock updates
Date: Tue, 14 May 2013 10:12:57 -0300 [thread overview]
Message-ID: <20130514131257.GA19277@amt.cnet> (raw)
In-Reply-To: <20130514090513.GB20995@redhat.com>
On Tue, May 14, 2013 at 12:05:13PM +0300, Gleb Natapov wrote:
> On Thu, May 09, 2013 at 08:21:41PM -0300, Marcelo Tosatti wrote:
> >
> > kvmclock updates which are isolated to a given vcpu, such as vcpu->cpu
> > migration, should not allow system_timestamp from the rest of the vcpus
> > to remain static. Otherwise ntp frequency correction applies to one
> > vcpu's system_timestamp but not the others.
> >
> > So in those cases, request a kvmclock update for all vcpus. The worst
> > case for a remote vcpu to update its kvmclock is then bounded by maximum
> > nohz sleep latency.
> >
> Does this mean that when one vcpu is migrated all others are kicked out
> from a guest mode?
Yes, those which are in guest mode. For guests with large number of
vcpus this is a problem, but i can't see a simpler method to fix the bug
for now.
Yes, this aspect must be improved (however, the bug incurs on timers in
the guest taking tens of milliseconds with vcpu->pcpu pinning, which can
be unacceptable).
next prev parent reply other threads:[~2013-05-14 13:13 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-09 23:21 KVM: x86: limit difference between kvmclock updates Marcelo Tosatti
2013-05-14 9:05 ` Gleb Natapov
2013-05-14 13:12 ` Marcelo Tosatti [this message]
2013-05-15 17:41 ` Gleb Natapov
2013-05-15 19:01 ` Marcelo Tosatti
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