From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1O6pHx-00081C-T5
	for qemu-devel@nongnu.org; Tue, 27 Apr 2010 14:13:41 -0400
Received: from [140.186.70.92] (port=42480 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1O6pHw-0007z0-8h
	for qemu-devel@nongnu.org; Tue, 27 Apr 2010 14:13:41 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69)
	(envelope-from <anthony@codemonkey.ws>) id 1O6pHu-0002rf-AO
	for qemu-devel@nongnu.org; Tue, 27 Apr 2010 14:13:40 -0400
Received: from mail-qy0-f188.google.com ([209.85.221.188]:55622)
	by eggs.gnu.org with esmtp (Exim 4.69)
	(envelope-from <anthony@codemonkey.ws>) id 1O6pHu-0002rU-4F
	for qemu-devel@nongnu.org; Tue, 27 Apr 2010 14:13:38 -0400
Received: by qyk26 with SMTP id 26so7376272qyk.19
	for <qemu-devel@nongnu.org>; Tue, 27 Apr 2010 11:13:37 -0700 (PDT)
Message-ID: <4BD72949.2070002@codemonkey.ws>
Date: Tue, 27 Apr 2010 13:13:29 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
References: <1272371652-23087-11-git-send-email-amit.shah@redhat.com>
	<1272371652-23087-12-git-send-email-amit.shah@redhat.com>
	<1272371652-23087-13-git-send-email-amit.shah@redhat.com>
	<1272371652-23087-14-git-send-email-amit.shah@redhat.com>
	<1272371652-23087-15-git-send-email-amit.shah@redhat.com>
	<1272371652-23087-16-git-send-email-amit.shah@redhat.com>
	<1272371652-23087-17-git-send-email-amit.shah@redhat.com>
	<1272371652-23087-18-git-send-email-amit.shah@redhat.com>
	<1272371652-23087-19-git-send-email-amit.shah@redhat.com>
	<4BD721C7.8010102@codemonkey.ws> <20100427175835.GA28137@amt.cnet>
In-Reply-To: <20100427175835.GA28137@amt.cnet>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Subject: [Qemu-devel] Re: [PATCH v6 18/18] virtio-serial-bus: wake up
 iothread upon guest read notification
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: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Amit Shah <amit.shah@redhat.com>, qemu list <qemu-devel@nongnu.org>, Juan Quintela <quintela@redhat.com>

On 04/27/2010 12:58 PM, Marcelo Tosatti wrote:
> On Tue, Apr 27, 2010 at 12:41:27PM -0500, Anthony Liguori wrote:
>    
>> On 04/27/2010 07:34 AM, Amit Shah wrote:
>>      
>>> From: Marcelo Tosatti<mtosatti@redhat.com>
>>>
>>> Wake up iothread when buffers are consumed.
>>>
>>> Signed-off-by: Marcelo Tosatti<mtosatti@redhat.com>
>>> Signed-off-by: Amit Shah<amit.shah@redhat.com>
>>>        
>> What's the race here?  This looks very odd to me.
>>      
> We discussed this on the following thread:
>
> http://www.mail-archive.com/kvm@vger.kernel.org/msg29249.html
>    

I don't think there was ever an adequate explanation of exactly what was 
happening.

My suspicion is that the real problem is due to the can_read() handlers 
whereas it's necessary to invoke the main loop for can_read() to be 
executed again to cause the event to be polled.  The better solution 
though is to not use the can_read() handler and instead explicitly 
register and deregister the read callbacks.

qemu_set_fd_handler() would require a notify call but that makes sense.

I think this is a good justification for removing uses of 
qemu_set_fd_handler2().

Regards,

Anthony Liguori