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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/

  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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