From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.saout.de ([127.0.0.1]) by localhost (mail.saout.de [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Mz7CgVFK30V1 for ; Wed, 14 Sep 2011 17:15:46 +0200 (CEST) Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by mail.saout.de (Postfix) with ESMTP for ; Wed, 14 Sep 2011 17:15:44 +0200 (CEST) Message-ID: <4E70C51D.5090501@redhat.com> Date: Wed, 14 Sep 2011 17:15:41 +0200 From: Milan Broz MIME-Version: 1.0 References: <4E70B46C.9050304@gmail.com> In-Reply-To: <4E70B46C.9050304@gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [dm-crypt] slow read performance, but fast writes? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Merhaut Cc: dm-crypt@saout.de On 09/14/2011 04:04 PM, Peter Merhaut wrote: > i've got a really strange problem with my setup, and i'm not quite sure why. It is known problem, current implementation depends on how are IO submitted and writes and reads differs this way (I think page cache interferes here). Reads are slower, because parallel operations are timed differently causing these waits. If you use some more realistic IO pattern than dd, you can get different output though. (dd is NOT good performance test. But everyone uses that:-) We have some ideas how to improve parallel processing inside dm-crypt but other things had higher priority still. (You can see this problem even measured against zero virtual devices, so read/write caching is not the real problem here.) Milan