From: Gerd Hoffmann <kraxel@redhat.com>
To: Glauber Costa <glommer@gmail.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
Avi Kivity <avi@qumranet.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
kvm-devel <kvm-devel@lists.sourceforge.net>
Subject: Re: Use of barriers in pvclock ABI
Date: Mon, 11 Aug 2008 16:49:13 +0200 [thread overview]
Message-ID: <48A05169.2090303@redhat.com> (raw)
In-Reply-To: <5d6222a80808110718i6a600858v7bdb5e08054ebefa@mail.gmail.com>
Glauber Costa wrote:
> On Mon, Aug 11, 2008 at 4:08 AM, Gerd Hoffmann <kraxel@redhat.com> wrote:
>> Due to the TSC being involved here I don't expect cross-cpu time updates
>> will ever happen. IMHO it is fine to change that.
>
> Okay for guest vcpu, but what about physical cpus?
>
> IIRC, the checks are there, and so strict, to account for the
> possiblity of the vcpu to be migrated to another cpu in the middle of
> the
> clock reading.
This is about the check in pvclock_get_time_values() that it got a
consistent snapshot. Dropping that is fine.
pvclock_clocksource_read() will still notice when being migrated to
another pcpu in the middle of the clock reading.
cheers,
Gerd
--
http://kraxel.fedorapeople.org/xenner/
next prev parent reply other threads:[~2008-08-11 14:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-08-08 19:51 Use of barriers in pvclock ABI Jeremy Fitzhardinge
2008-08-11 7:08 ` Gerd Hoffmann
2008-08-11 14:15 ` Avi Kivity
2008-08-11 14:18 ` Glauber Costa
2008-08-11 14:35 ` Avi Kivity
2008-08-11 14:49 ` Gerd Hoffmann [this message]
2008-08-11 16:02 ` Jeremy Fitzhardinge
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