Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751905AbXBVVZK (ORCPT ); Thu, 22 Feb 2007 16:25:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751910AbXBVVZJ (ORCPT ); Thu, 22 Feb 2007 16:25:09 -0500 Received: from agminet01.oracle.com ([141.146.126.228]:49017 "EHLO agminet01.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751905AbXBVVZI (ORCPT ); Thu, 22 Feb 2007 16:25:08 -0500 In-Reply-To: <20070222074044.GA4158@elte.hu> References: <20070221211355.GA7302@elte.hu> <20070221233111.GB5895@elte.hu> <45DCD9E5.2010106@redhat.com> <20070222074044.GA4158@elte.hu> Mime-Version: 1.0 (Apple Message framework v752.3) Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: Cc: Ulrich Drepper , linux-kernel@vger.kernel.org, Linus Torvalds , Arjan van de Ven , Christoph Hellwig , Andrew Morton , Alan Cox , Evgeniy Polyakov , "David S. Miller" , Suparna Bhattacharya , Davide Libenzi , Jens Axboe , Thomas Gleixner Content-Transfer-Encoding: 7bit From: Zach Brown Subject: Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3 Date: Thu, 22 Feb 2007 13:23:57 -0800 To: Ingo Molnar X-Mailer: Apple Mail (2.752.3) X-Brightmail-Tracker: AAAAAQAAAAI= X-Whitelist: TRUE Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1806 Lines: 50 > Plus there's the fundamental killer that KAIO is a /lot/ harder to > implement (and to maintain) on the kernel side: it has to be > implemented > for every IO discipline, and even for the IO disciplines it > supports at > the moment, it is not truly asynchronous for things like metadata > blocking or VFS blocking. To handle things like metadata blocking > it has > to resort to non-statemachine techniques like retries - which are bad > for performance. Yes, yes, yes. As one of the poor suckers who has been fixing bugs in fs/aio.c and fs/direct-io.c, I really want everyone to read Ingo's paragraph a few times. Have it printed on a t-shirt. Look at the number of man-years that have gone into fs/aio.c and fs/ direct-io.c. After all that effort it *barely* supports non-blocking O_DIRECT IO. The maintenance overhead of those two files, above all else, is what pushed me to finally try that nutty fibril attempt. > Syslets/threadlets on the other hand, once the core is implemented, > have > near zero ongoing maintainance cost (compared to KAIO pushed into > every > IO subsystem) and cover all IO disciplines and API variants > immediately, > and they are as perfectly asynchronous as it gets. Amen. As an experiment, I'm working on backing the sys_io_*() calls with syslets. It's looking very promising so far. > So all in one, i used to think that AIO state-machines have a long- > term > place within the kernel, but with syslets i think i've proven myself > embarrasingly wrong =B-) Welcome to the party :). - z - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/