From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:54110)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <jan.kiszka@siemens.com>) id 1R8Yn5-00088I-PS
	for qemu-devel@nongnu.org; Tue, 27 Sep 2011 10:37:48 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <jan.kiszka@siemens.com>) id 1R8Ymz-0004O5-3y
	for qemu-devel@nongnu.org; Tue, 27 Sep 2011 10:37:47 -0400
Received: from david.siemens.de ([192.35.17.14]:30578)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <jan.kiszka@siemens.com>) id 1R8Ymy-0004Nn-Hx
	for qemu-devel@nongnu.org; Tue, 27 Sep 2011 10:37:40 -0400
Message-ID: <4E81DF7C.4080403@siemens.com>
Date: Tue, 27 Sep 2011 16:36:44 +0200
From: Jan Kiszka <jan.kiszka@siemens.com>
MIME-Version: 1.0
References: <4E78C42D.5030207@siemens.com>
	<20110921080600.GA9847@stefanha-thinkpad.localdomain>
	<4E80B50B.9000301@siemens.com> <4E80B55F.5020203@redhat.com>
	<4E80BFF3.8000907@us.ibm.com> <4E8190BE.3000801@redhat.com>
	<4E81D609.1060203@siemens.com> <4E81D88B.4020504@codemonkey.ws>
	<4E81DDDF.8050201@siemens.com> <4E81DEEA.10208@redhat.com>
In-Reply-To: <4E81DEEA.10208@redhat.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH] Use qemu_eventfd for POSIX AIO
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: Avi Kivity <avi@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, Marcelo Tosatti <mtosatti@redhat.com>, qemu-devel <qemu-devel@nongnu.org>

On 2011-09-27 16:34, Avi Kivity wrote:
> On 09/27/2011 05:29 PM, Jan Kiszka wrote:
>>>
>>>  Moreover, the eventfd() counter is not lossy (practically speaking) whereas if
>>>  you use pipe() as a counter, it will be lossy in practice.
>>>
>>>  This is why posix aio uses pipe() and not eventfd().
>>
>> I don't get this yet. eventfd is lossy by default. It only decreases the
>> counter on read if you specify EFD_SEMAPHORE - which we do not do.
>>
> 
> It's not lossy - a read returns the number of events written since the 
> last read.

Yeah, but what's the point? We don't evaluate this.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux