From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756106AbZHGVSO (ORCPT ); Fri, 7 Aug 2009 17:18:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755709AbZHGVSN (ORCPT ); Fri, 7 Aug 2009 17:18:13 -0400 Received: from mailhost14.gawab.com ([66.220.20.14]:35930 "HELO info88.gawab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1755437AbZHGVSM (ORCPT ); Fri, 7 Aug 2009 17:18:12 -0400 X-Trusted: Whitelisted From: Al Boldi To: "Chris Friesen" , Greg KH Subject: Re: [PATCH] Driver Core: devtmpfs - kernel-maintained tmpfs-based /dev Date: Sat, 8 Aug 2009 00:17:31 +0300 User-Agent: KMail/1.5 Cc: Andi Kleen , Alan Cox , linux-kernel@vger.kernel.org, Kay Sievers , Jan Blunck , gregkh@suse.de, Harald Hoyer , Scott James Remnant References: <20090805171513.GA10443@kroah.com> <20090807052015.GA24615@kroah.com> <4A7C4D6C.6050101@nortel.com> In-Reply-To: <4A7C4D6C.6050101@nortel.com> MIME-Version: 1.0 Content-Disposition: inline Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <200908080017.31376.a1426z@gawab.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Chris Friesen wrote: > Greg KH wrote: > > On Fri, Aug 07, 2009 at 08:04:08AM +0300, Al Boldi wrote: > >> The question is, how fast can devtmpfs get the device list from the > >> kernel on bootup? How much faster than udev? How much slower than > >> static /dev? > > > > It's much faster than udev, and is equivalent to a static /dev with the > > exception that the group and permission settings that you are used to. > > udev then needs to come along and make those settings, but that's so > > frickin fast it's amazing. > > Earlier in the thread you indicated a 0.5sec speedup over udev. Is that > really considered "much faster"? > > I do agree that it makes sense to do this, but more from an elegance > view than a performance one. It's definitely more elegant, but at what cost? For devtmpfs to be a realistic replacement for static /dev, it has to be comparable to static /dev in both speed and size. WRT speed, there should be no slowdown and it should be just as fast as a "tar -xp < dev.tar". WRT size, it should not be dependent on hotplug, and instead offer hotplug as an option. Thanks! -- Al