Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755608Ab1E3VYq (ORCPT ); Mon, 30 May 2011 17:24:46 -0400 Received: from mail-pv0-f174.google.com ([74.125.83.174]:33760 "EHLO mail-pv0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753993Ab1E3VYo convert rfc822-to-8bit (ORCPT ); Mon, 30 May 2011 17:24:44 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=SUP6JnLmlJsF3vDYe3oo+knlChYuMP3yGFOuCFS8tKxKWpKVV+u2KiXg1gj4gvCmI7 teffqZn5y1Q7a52hfpz+HPgJKUWH84mu/T9yy8ae9fH3AzB8MK89PApGxweIp8TzdZxa K0Clyf+UDU8MAKRS6+/oQJqC4W2B3zlcqbWm0= MIME-Version: 1.0 In-Reply-To: References: <201105231012.06928.oneukum@suse.de> <20110525000003.GJ32466@dastard> <201105250850.12179.oneukum@suse.de> <410B37BE-E380-40D0-82AA-48B56F389E16@mit.edu> <20110526133155.GH9520@thunk.org> <20110526162138.GN9520@thunk.org> From: "D. Jansen" Date: Mon, 30 May 2011 23:24:03 +0200 Message-ID: Subject: Re: [rfc] Ignore Fsync Calls in Laptop_Mode To: david@lang.hm Cc: Theodore Tso , Oliver Neukum , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Dave Chinner , njs@pobox.com, bart@samwel.tk 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 Content-Length: 2993 Lines: 70 On Mon, May 30, 2011 at 10:53 PM, wrote: > On Mon, 30 May 2011, D. Jansen wrote: > >> On Mon, May 30, 2011 at 8:45 PM,   wrote: >>> >>> >>> the problem is that most users don't know what their system is running, >>> or >>> what effect disaling fsync would have. those that do can probably use >>> LD_PRELOAD to override fsync calls. >> >> As we found out, they can't. But if we export barrier, I hope a >> library could wrap fsyncs into barriers. Is that the case? > > a library can wrap fsync into anything. > >>> >>> it doesn't take running a mail server, even a mail client will have the >>> same >>> risk. If you use POP for mail (a very common option) then you download >>> messages and tell the server to delete them. if you do not really save >>> them >>> (one fsync after they are all saved), then you can loose everything that >>> you >>> downloaded. >> >> Yes, I know. It's the same argument again and again. I understand not >> everybody wants this. But some do. Some prefer working 10-20% longer >> on battery (certainty) instead of possibly losing 5 % data >> (possibility) or losing all your data (possibility if you use laptop >> mode and the hard disk wakes up again and again and eventually wears >> out). > > those are some powerful numbers you are throwing around, can you back them > up? Yes. My netbook uses 4.8 W with hard disk off. 0.5 W more with hard disk on. A lot of the time, the display is off and the power consumption drops to about 3.5 W. I don't know how I got to 20 % atm. I can only do this if fsync is disabled. I tried before, but it would go on for every write. It died, very prematurely. > > do you really have so many fsync's going on that the disk spins up so much > that you would gain 10-20% battery life? Yes. Every autosave in LibreOffice triggers one. And I want autosave, but I want them in memory, not on disk. > > and what makes you think the extra spin-ups from fsyncs will cause your hard > drive to fail significantly earlier? (if you have a hard drive with a > limited number of spin-up cycles, you probably don't want to use laptop mode > at all) Experience, see above. Also, this is well described behavior. All hard disks are only designed to last a certain number of head loads and unloads. Spinning up and down even less. > > why do you think it's a possibility of loosing only 5% of data? Well, it really depends on the way your configure laptop mode. But in my case the laptop mode window is 20 minutes, the run time then is about 10-12 hrs. I can actually lose less than 5 % of the data created during the battery run time. It's a certain 1-1.5 hours (10-15 %) more work or a possible 20 mins (3.3 % actually) loss of work. I think it's a good deal. -- 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/