From owner-freebsd-virtualization@FreeBSD.ORG  Wed Sep 25 15:05:47 2013
Return-Path: <owner-freebsd-virtualization@FreeBSD.ORG>
Delivered-To: virtualization@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTP id AC693A11;
 Wed, 25 Sep 2013 15:05:47 +0000 (UTC)
 (envelope-from roger.pau@citrix.com)
Received: from SMTP.CITRIX.COM (smtp.citrix.com [66.165.176.89])
 (using TLSv1 with cipher RC4-SHA (128/128 bits))
 (No client certificate requested)
 by mx1.freebsd.org (Postfix) with ESMTPS id CA7192C36;
 Wed, 25 Sep 2013 15:05:46 +0000 (UTC)
X-IronPort-AV: E=Sophos;i="4.90,978,1371081600"; d="scan'208";a="57286431"
Received: from accessns.citrite.net (HELO FTLPEX01CL01.citrite.net)
 ([10.9.154.239])
 by FTLPIPO01.CITRIX.COM with ESMTP; 25 Sep 2013 15:04:35 +0000
Received: from [IPv6:::1] (10.80.16.47) by smtprelay.citrix.com (10.13.107.78)
 with Microsoft SMTP Server id 14.2.342.4;
 Wed, 25 Sep 2013 11:04:35 -0400
Message-ID: <5242FB81.4090002@citrix.com>
Date: Wed, 25 Sep 2013 17:04:33 +0200
From: =?ISO-8859-1?Q?Roger_Pau_Monn=E9?= <roger.pau@citrix.com>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7;
 rv:17.0) Gecko/20130801 Thunderbird/17.0.8
MIME-Version: 1.0
To: Julian Elischer <julian@freebsd.org>
Subject: Re: Xen (and others Hypervisors) how do they handle IPIs?
References: <5242F9B8.9090300@freebsd.org>
In-Reply-To: <5242F9B8.9090300@freebsd.org>
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7bit
X-DLP: MIA1
Cc: virtualization@FreeBSD.org
X-BeenThere: freebsd-virtualization@freebsd.org
X-Mailman-Version: 2.1.14
Precedence: list
List-Id: "Discussion of various virtualization techniques FreeBSD supports."
 <freebsd-virtualization.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-virtualization>, 
 <mailto:freebsd-virtualization-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-virtualization>
List-Post: <mailto:freebsd-virtualization@freebsd.org>
List-Help: <mailto:freebsd-virtualization-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-virtualization>, 
 <mailto:freebsd-virtualization-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 25 Sep 2013 15:05:47 -0000

On 25/09/13 16:56, Julian Elischer wrote:
> If CPUs are mapped around, how are IPIs handled? I assume they must be
> emulated?
> 
> I've noticed that under Xen (on both Amazon EC2 and a Redhat server)
> whenever you schedule a thread it always sits on the run queue for 20
> uSecs before it starts running. It looks to me like it's the IPI taking
> a long time to be emulated.

This has been improved on the FreeBSD Xen PVHVM port by using PV IPIs
instead of the emulated ones, see r255331. It should be faster than the
previous emulated implementation.