From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1NvBNP-0005bG-QA
	for qemu-devel@nongnu.org; Fri, 26 Mar 2010 11:23:11 -0400
Received: from [140.186.70.92] (port=38005 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1NvBNO-0005Zs-LO
	for qemu-devel@nongnu.org; Fri, 26 Mar 2010 11:23:11 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69)
	(envelope-from <paul@codesourcery.com>) id 1NvBNM-00009L-PW
	for qemu-devel@nongnu.org; Fri, 26 Mar 2010 11:23:10 -0400
Received: from mx20.gnu.org ([199.232.41.8]:58776)
	by eggs.gnu.org with esmtp (Exim 4.69)
	(envelope-from <paul@codesourcery.com>) id 1NvBNM-00009H-Mw
	for qemu-devel@nongnu.org; Fri, 26 Mar 2010 11:23:08 -0400
Received: from mail.codesourcery.com ([38.113.113.100])
	by mx20.gnu.org with esmtp (Exim 4.60)
	(envelope-from <paul@codesourcery.com>) id 1NvBNM-00005E-5r
	for qemu-devel@nongnu.org; Fri, 26 Mar 2010 11:23:08 -0400
From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [patch 1/2] Pass QEMUIOWorker to qemu_notify_event
Date: Fri, 26 Mar 2010 15:23:03 +0000
References: <20100325134715.354365213@amt.cnet>
	<201003252106.01194.paul@codesourcery.com>
	<20100326035558.GA20616@amt.cnet>
In-Reply-To: <20100326035558.GA20616@amt.cnet>
MIME-Version: 1.0
Content-Type: Text/Plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Message-Id: <201003261523.03617.paul@codesourcery.com>
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org
Cc: amit.shah@redhat.com, Anthony Liguori <aliguori@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>

> On Thu, Mar 25, 2010 at 09:06:00PM +0000, Paul Brook wrote:
> > >  /* Force QEMU to process pending events */
> > > -void qemu_notify_event(void);
> > > +void qemu_notify_event(QEMUIOWorker *worker);
> > >
> > >  static void handle_input(VirtIODevice *vdev, VirtQueue *vq)
> > >  {
> > > +    qemu_notify_event(main_io_worker);
> > >  }
> >
> > This feels completely wrong.
> >
> > Devices shouldn't know or care about implementation details like this.
> > How is a device supposed to know which worker it should be waking up?
> 
> Its not. It could use qemu_notify_event(DeviceInfo->worker), and have no
> knowledge of the internals.

In that case I think you're abusing this API.

I'm very wary of introducing random bits of code that allegedly allow future 
use of threads.  Exploiting thread level parallelism is a hard problem that 
needs proper design.  A such I object to this patch, and think we first need 
to decide what form of concurrency model we want to use in QEMU.

Paul