From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756591Ab0CJNV4 (ORCPT ); Wed, 10 Mar 2010 08:21:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:64042 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756484Ab0CJNVy (ORCPT ); Wed, 10 Mar 2010 08:21:54 -0500 From: Jeff Moyer To: M vd S Cc: linux-kernel@vger.kernel.org Subject: Re: O_NONBLOCK is NOOP on block devices References: <4B904D98.50602@gmail.com> <4B9060DE.4080104@gmail.com> <4B96ECDD.1070006@gmail.com> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Wed, 10 Mar 2010 08:21:51 -0500 In-Reply-To: <4B96ECDD.1070006@gmail.com> (M. vd S.'s message of "Wed, 10 Mar 2010 01:50:37 +0100") Message-ID: User-Agent: Gnus/5.110011 (No Gnus v0.11) Emacs/23.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org M vd S writes: > I also briefly tried aio_* and the libaio interface. The former is not > really asynchronous - all requests are put in one separate thread > where they will be executed in order, i.e. blocking, so you don't get > any advantage from NCQ or data that was cached by the disk or the > kernel. The latter apparently ends in an io_submit() which will block > until all queued reads are finished, but I might have missed something > there. What you missed is that the native aio system calls require O_DIRECT. Cheers, Jeff