From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753843AbZEISKJ (ORCPT ); Sat, 9 May 2009 14:10:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753209AbZEISJ5 (ORCPT ); Sat, 9 May 2009 14:09:57 -0400 Received: from mail-bw0-f174.google.com ([209.85.218.174]:43973 "EHLO mail-bw0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753161AbZEISJ4 convert rfc822-to-8bit (ORCPT ); Sat, 9 May 2009 14:09:56 -0400 MIME-Version: 1.0 In-Reply-To: <20090509181138.15d2a490@lxorguk.ukuu.org.uk> References: <20090509143742.GA27663@kroah.com> <20090509150853.GA32394@suse.de> <20090509082233.32cbb8e4@infradead.org> <20090509181138.15d2a490@lxorguk.ukuu.org.uk> From: Kay Sievers Date: Sat, 9 May 2009 20:09:35 +0200 Message-ID: Subject: Re: [patch 00/13] devtmpfs patches To: Alan Cox Cc: Arjan van de Ven , Greg KH , Fabio Comolli , Greg KH , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 9, 2009 at 19:11, Alan Cox wrote: > On Sat, 9 May 2009 18:46:10 +0200 > Kay Sievers wrote: > >> On Sat, May 9, 2009 at 17:22, Arjan van de Ven wrote: >> > On Sat, 9 May 2009 08:08:53 -0700 >> > Greg KH wrote: >> > >> >> > Well, guess you meant the opposite ;-) >> >> >> >> Heh, yes, sorry about that.  It makes booting faster :) >> > >> > .. and I don't buy that. >> >> Don't buy, just try it - and you will see. :) > > Got some boot timing graphs for the change ? So far, I got numbers for different options used with devtmpfs to compare initramfs with non-initramfs. Initramfs is what all general purpose distros need to use today, to be able to identify the disk by LABEL/UUID/Hardware-properties. And I wanted to see how expensive the use of initramfs is. They are posted here: http://lkml.org/lkml/2009/5/6/197 The "init" for intramfs is attached to the mail, mainly to illustrate the simplification over the things we need to do today, and that there is never a point in time where we have to delay things, because /dev is empty during the moment we mount a fresh and empty tmpfs /dev. To directly compare numbers for devtmpfs and non-devtmpfs, the "init" script would need to be modified to ignore the kernel provided devtmpfs and mount an empty tmpfs over it, and populate it, just like we do it today. There is no theoretical chance that this can ever be faster. Most of the bootstrap logic we have today: mount an empty tmpfs /dev -> add the few mandatory nodes to be able to start the bootstrap process -> run something that reads sysfs-device-information (in the usual case udev) -> delaying all further processing until /dev is minimally usable to start things that rely on a working /dev, ... all that gets basically stripped down to: "mount --move /dev /root/dev", right at the end before we leave initramfs behind us. Kay