From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from tansi.org (ns.km10532-04.keymachine.de [87.118.102.195]) by mail.saout.de (Postfix) with ESMTP for ; Thu, 17 Sep 2009 13:12:50 +0200 (CEST) Received: from gatewagner.dyndns.org (84-74-165-216.dclient.hispeed.ch [84.74.165.216]) by tansi.org (Postfix) with ESMTP id 265324250006 for ; Thu, 17 Sep 2009 13:12:50 +0200 (CEST) Date: Thu, 17 Sep 2009 13:12:47 +0200 From: Arno Wagner Message-ID: <20090917111247.GA31882@tansi.org> References: <20090916081108.GB8804@tansi.org> <20090916215427.GA20647@tansi.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [dm-crypt] md-raid5+lvm+dm-crypt+kvm: one streaming write starves all reads List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: dm-crypt@saout.de On Thu, Sep 17, 2009 at 02:36:39AM +0200, Christian Pernegger wrote: > > Hmm. So without dm-crypt no problem? The main effect of dm-crypt > > is to make the disk appear slower, because of the encryption. > > Unfortunately it's not *just* slower. Yes, the arrays would be 2x-3x > as fast without encryption, but that's not the point. It's that I/O > bandwidth isn't shared fairly at all. As if all crypt requests went > into one big FIFO ... (But then, maybe they do.) The stream with the > most/biggest requests then gets all the bandwidth. Yes. And that may be some s"synergetic" effect triggered by the slowness. At least that is one possible explanation. > > You could try this with a dummy-cipher that does not take encryption time. > > Excellent idea, what's the cipher string for that? I couldn't find > anything obvious in /proc/crypto or under > /lib/modules/.../kernel/crypto/. I have not tried this myself, but hit candidates are "ciper_null" and "ecb(ciper_null)". I have both (kernel 2.6.30.5) Arno -- Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F ---- Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans If it's in the news, don't worry about it. The very definition of "news" is "something that hardly ever happens." -- Bruce Schneier