From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:59982)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <xerox.time.tech@gmail.com>) id 1RNkvg-0004Xt-Fg
	for qemu-devel@nongnu.org; Tue, 08 Nov 2011 07:37:29 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <xerox.time.tech@gmail.com>) id 1RNkve-0007Dj-OB
	for qemu-devel@nongnu.org; Tue, 08 Nov 2011 07:37:28 -0500
Received: from mail-iy0-f173.google.com ([209.85.210.173]:52082)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <xerox.time.tech@gmail.com>) id 1RNkve-0007DX-Ju
	for qemu-devel@nongnu.org; Tue, 08 Nov 2011 07:37:26 -0500
Received: by iakk32 with SMTP id k32so530289iak.4
	for <qemu-devel@nongnu.org>; Tue, 08 Nov 2011 04:37:26 -0800 (PST)
MIME-Version: 1.0
In-Reply-To: <CAJSP0QWXL2k-xMvGz_85cnwDdSSzCLGai+mOmEpOLeszpxUHxw@mail.gmail.com>
References: <CALKntY1_5x4iaVTcE0JW=k17ohDFQ-ALdYKj65s8-eJW9x7rkA@mail.gmail.com>
	<20111108120443.GA76806@cs.nctu.edu.tw>
	<20111108121056.GA96832@cs.nctu.edu.tw>
	<CAJSP0QWXL2k-xMvGz_85cnwDdSSzCLGai+mOmEpOLeszpxUHxw@mail.gmail.com>
Date: Tue, 8 Nov 2011 07:37:25 -0500
Message-ID: <CALKntY2E7zjTB=qf5H7xzR8B+sx2-We0Y_gDfcGwzjo3hFEa5Q@mail.gmail.com>
From: Xin Tong <xerox.time.tech@gmail.com>
Content-Type: text/plain; charset=Big5
Content-Transfer-Encoding: quoted-printable
Subject: Re: [Qemu-devel] multiprocessor on kvm
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: qemu-devel <qemu-devel@nongnu.org>, =?UTF-8?B?6Zmz6Z+L5Lu7?= <chenwj@iis.sinica.edu.tw>

so qemu exposes multiple processors to the guest os by having multiple
vCPUs. and it realizes the multiple vCPUs by either using RR on a
single host cpu (qemu ) or using multiple host cpus (kvm).

Thanks

Xin


2011/11/8 Stefan Hajnoczi <stefanha@gmail.com>:
> On Tue, Nov 8, 2011 at 12:10 PM, =B3=AF=AD=B3=A5=F4 <chenwj@iis.sinica.ed=
u.tw> wrote:
>> On Tue, Nov 08, 2011 at 08:04:44PM +0800, =B3=AF=AD=B3=A5=F4 wrote:
>>> > I am wondering that when one uses qemu with kvm. How many cores are
>>> > exposed and available to the guest os ( assuming the host has 4 cores
>>> > ). is this configurable ?
>>>
>>>   QEMU provides "-smp" option, but those virtual cpus are scheduled in
>>> round-robin fashion. In other words, it's not real parallelism. I don't
>>> know if there is any difference with kvm enabled.
>>
>>  IIRC, kvm uses QEMU for device emulation only. Those virtual cpus are
>> ran on physical cpus simultaneously.
>
> Right, qemu -enable-kvm will run a thread for each vCPU.  So you get
> true SMP parallelism.
>
> QEMU without KVM mode, on the other hand, does round-robin scheduling
> of vCPUs and does not take advantage of multiprocessor hosts.
>
> Stefan
>