Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751544AbXB1QRJ (ORCPT ); Wed, 28 Feb 2007 11:17:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751564AbXB1QRI (ORCPT ); Wed, 28 Feb 2007 11:17:08 -0500 Received: from x35.xmailserver.org ([64.71.152.41]:4697 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751544AbXB1QRH (ORCPT ); Wed, 28 Feb 2007 11:17:07 -0500 X-AuthUser: davidel@xmailserver.org Date: Wed, 28 Feb 2007 08:17:01 -0800 (PST) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Ingo Molnar cc: Ulrich Drepper , Linux Kernel Mailing List , Linus Torvalds , Arjan van de Ven , Christoph Hellwig , Andrew Morton , Alan Cox , Zach Brown , Evgeniy Polyakov , "David S. Miller" , Suparna Bhattacharya , Jens Axboe , Thomas Gleixner Subject: Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3 In-Reply-To: <20070228094522.GA17716@elte.hu> Message-ID: References: <20070221211355.GA7302@elte.hu> <20070221233111.GB5895@elte.hu> <45DCD9E5.2010106@redhat.com> <20070222074044.GA4158@elte.hu> <20070228094522.GA17716@elte.hu> X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2158 Lines: 45 On Wed, 28 Feb 2007, Ingo Molnar wrote: > > * Davide Libenzi wrote: > > > Why can't aio_* be implemented with *simple* (or parallel/unrelated) > > syscall submit w/out the burden of a complex, limiting and heavy API > > there are so many variants of what people think 'asynchronous IO' should > look like - i'd not like to limit them. I agree that once a particular > syslet script becomes really popular, it might (and should) in fact be > pushed into a separate system call. > > But i also agree that a one-shot-syscall sys_async() syscall could be > done too - for those uses where only a single system call is needed and > where the fetching of a single uatom would be small but nevertheless > unnecessary overhead. A one-shot async syscall needs to get /8/ > parameters (the syscall nr is the seventh parameter and the return code > of the nested syscall is the eighth). So at least two parameters will > have to be passed in indirectly and validated, and 32/64-bit compat > conversions added, etc. anyway! At this point, given how threadlets can be easily/effectively dispatched from userspace, I'd argue the presence of either single/parallel or syslet submission altogether. Threadlets allows you to code chains *way* more naturally than syslets, and since they basically are like functions calls in the fast path, they can be used even for single/parallel submissions. No compat code required (ok, besides the trivial async_wait). My point is, the syslet infrastructure is expensive for the kernel in terms of compat, and extra code added to handle the cond/jumps/etc. Is also non-trivial to use from userspace. Are those big performance advantages there to justify its existence? I doubt that the price of a sysenter is a lot bigger than a atom decoding, but I'm looking forward in being proven wrong by real life performance numbers ;) - Davide - 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/