All of lore.kernel.org
 help / color / mirror / Atom feed
From: Jiri Denemark <jdenemar@redhat.com>
To: "Peter Huang(Peng)" <peter.huangpeng@huawei.com>
Cc: libvir-list@redhat.com, Eduardo Habkost <ehabkost@redhat.com>,
	qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [Question] why x2apic's set by default without host support(on Nehalem CPU).
Date: Tue, 23 Jul 2013 13:27:12 +0200	[thread overview]
Message-ID: <20130723112712.GF4718@orkuz.home> (raw)
In-Reply-To: <51EDEE20.4060206@huawei.com>

On Tue, Jul 23, 2013 at 10:44:48 +0800, Peter Huang(Peng) wrote:
> > libvirt's "host-passthrough" uses "-cpu host', and it "-cpu host"
> > enables every feature that can be enabled on the host.
> From my test results, I found that even when use host-passthrough mode, VM's
> cpu features are very different from host, this doesn't match what host-passthrough
> mode's explanation.
> 
> libvirt's option exlanation:
> With this mode, the CPU visible to the guest should be exactly  the  same as  the host 
> CPU even in  the aspects  that libvirt  does not understand.

The libvirt documentation is what needs to be updated. While
host-passthrough is asking for a CPU which is as close as possible to
the real host CPU, there are features that need special handling before
they can be provided to a guest. And if the hypervisor does not provide
that handling, it may just filter such feature out. Also if some
features can be efficiently provided to a guest even though the host CPU
does not provide them (x2apic is an example of such feature), they may
be provided to a guest.

Jirka

  reply	other threads:[~2013-07-23 11:37 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-22 11:24 [Qemu-devel] [Question] why x2apic's set by default without host support(on Nehalem CPU) Peter Huang(Peng)
2013-07-22 12:36 ` Peter Huang(Peng)
2013-07-22 12:36   ` [Qemu-devel] " Peter Huang(Peng)
2013-07-22 23:55   ` Marcelo Tosatti
2013-07-22 23:55     ` [Qemu-devel] " Marcelo Tosatti
2013-07-23  2:38     ` Peter Huang(Peng)
2013-07-23  2:38       ` [Qemu-devel] " Peter Huang(Peng)
2013-07-22 13:41 ` Eduardo Habkost
2013-07-23  2:44   ` Peter Huang(Peng)
2013-07-23 11:27     ` Jiri Denemark [this message]
2013-07-24  0:48       ` Peter Huang(Peng)
2013-07-24  2:54         ` [Qemu-devel] [Solved]FYI//Re: " Peter Huang(Peng)

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20130723112712.GF4718@orkuz.home \
    --to=jdenemar@redhat.com \
    --cc=ehabkost@redhat.com \
    --cc=libvir-list@redhat.com \
    --cc=peter.huangpeng@huawei.com \
    --cc=qemu-devel@nongnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.