From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [PATCH] Implement an fd pool to get real AIO with posix-aio Date: Wed, 24 Sep 2008 09:17:07 -0500 Message-ID: <48DA4BE3.30403@us.ibm.com> References: <1222202051-26701-1-git-send-email-aliguori@us.ibm.com> <48DA021F.2050504@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: qemu-devel@nongnu.org, Ryan Harper , kvm To: Avi Kivity Return-path: Received: from e4.ny.us.ibm.com ([32.97.182.144]:53337 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751359AbYIXOSJ (ORCPT ); Wed, 24 Sep 2008 10:18:09 -0400 Received: from d01relay02.pok.ibm.com (d01relay02.pok.ibm.com [9.56.227.234]) by e4.ny.us.ibm.com (8.13.8/8.13.8) with ESMTP id m8OEI9vY000678 for ; Wed, 24 Sep 2008 10:18:09 -0400 Received: from d01av03.pok.ibm.com (d01av03.pok.ibm.com [9.56.224.217]) by d01relay02.pok.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id m8OEI8Yi286884 for ; Wed, 24 Sep 2008 10:18:08 -0400 Received: from d01av03.pok.ibm.com (loopback [127.0.0.1]) by d01av03.pok.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id m8OEI8wH011736 for ; Wed, 24 Sep 2008 10:18:08 -0400 In-Reply-To: <48DA021F.2050504@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > Anthony Liguori wrote: > > dup()ing the fd on each request is unnecessary work; would be better > to cache the duped fd. Yeah, I was concerned about this too. Ryan reran the fio benchmark and the submission latency and completion latency were identical to the linux-aio patches. That suggests that the overhead of dup() is lost in the noise. Since this is simpler and keeps the number of open file descriptors as low as possible, I was happy about that. Regards, Anthony Liguori > Of course, if this is just a stepping stone, it doesn't matter very much. >