From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [Qemu-devel] live migration vs device assignment (motivation)
Date: Mon, 28 Dec 2015 13:51:08 +0200
Message-ID: <20151228115108.GC18063@redhat.com>
References: <20151207165039.GA20210@redhat.com>
 <56685631.50700@intel.com>
 <20151210101840.GA2570@work-vm>
 <566961C1.6030000@gmail.com>
 <20151210114114.GE2570@work-vm>
 <56698E68.5040207@intel.com>
 <CAKgT0UduOMvnVAUvRgnXkMPDwvOBh_5RimCgnb0zRr7aOyza4A@mail.gmail.com>
 <566D9320.8000209@intel.com>
 <20151214112253-mutt-send-email-mst@redhat.com>
 <003a01d1414d$1f2fd250$5d8f76f0$@samsung.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: "'Lan, Tianyu'" <tianyu.lan@intel.com>,
	"'Yang Zhang'" <yang.zhang.wz@gmail.com>,
	"'Tantilov, Emil S'" <emil.s.tantilov@intel.com>,
	kvm@vger.kernel.org, aik@ozlabs.ru, qemu-devel@nongnu.org,
	"'Alexander Duyck'" <alexander.duyck@gmail.com>,
	lcapitulino@redhat.com, "'Blue Swirl'" <blauwirbel@gmail.com>,
	kraxel@redhat.com, "'Rustad, Mark D'" <mark.d.rustad@intel.com>,
	quintela@redhat.com,
	"'Skidmore, Donald C'" <donald.c.skidmore@intel.com>,
	"'Alexander Graf'" <agraf@suse.de>,
	"'Or Gerlitz'" <gerlitz.or@gmail.com>,
	"'Dr. David Alan Gilbert'" <dgilbert@redhat.com>,
	"'Alex Williamson'" <alex.williamson@redhat.com>,
	"'Anthony Liguori'" <anthony@codemonkey.ws>,
	cornelia.huck@de.ibm.com,
	"'Ard Biesheuvel'" <ard.biesheuvel@linaro.org>,
	"'Dong, Eddie'" <eddie.dong@intel.com>,
	"'Jani, Nrupal'" <nrupal.jani@intel.com>, amit.shah@redhat.com,
	"'Paolo Bonzini'" <pbonzini@redhat.co
To: Pavel Fedin <p.fedin@samsung.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:51768 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751584AbbL1LvQ (ORCPT <rfc822;kvm@vger.kernel.org>);
	Mon, 28 Dec 2015 06:51:16 -0500
Content-Disposition: inline
In-Reply-To: <003a01d1414d$1f2fd250$5d8f76f0$@samsung.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Mon, Dec 28, 2015 at 11:52:43AM +0300, Pavel Fedin wrote:
>  Hello!
> 
> > A dedicated IRQ per device for something that is a system wide event
> > sounds like a waste.  I don't understand why a spec change is strictly
> > required, we only need to support this with the specific virtual bridge
> > used by QEMU, so I think that a vendor specific capability will do.
> > Once this works well in the field, a PCI spec ECN might make sense
> > to standardise the capability.
> 
>  Keeping track of your discussion for some time, decided to jump in...
>  So far, we want to have some kind of mailbox to notify the quest about migration. So what about some dedicated "pci device" for
> this purpose? Some kind of "migration controller". This is:
> a) perhaps easier to implement than capability, we don't need to push anything to PCI spec.
> b) could easily make friendship with Windows, because this means that no bus code has to be touched at all. It would rely only on
> drivers' ability to communicate with each other (i guess it should be possible in Windows, isn't it?)
> c) does not need to steal resources (BARs, IRQs, etc) from the actual devices.
> 
> Kind regards,
> Pavel Fedin
> Expert Engineer
> Samsung Electronics Research center Russia
> 

Sure, or we can use an ACPI device.  It doesn't really matter what we do
for the mailbox. Whoever writes this first will get to select a
mechanism.

-- 
MST