From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Priebe - Profihost AG Subject: Re: extreme ceph-osd cpu load for rand. 4k write Date: Thu, 08 Nov 2012 15:58:00 +0100 Message-ID: <509BC878.3090804@profihost.ag> References: <509AC772.5010606@profihost.ag> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail.profihost.ag ([85.158.179.208]:58763 "EHLO mail.profihost.ag" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751692Ab2KHO6J (ORCPT ); Thu, 8 Nov 2012 09:58:09 -0500 In-Reply-To: <509AC772.5010606@profihost.ag> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: "ceph-devel@vger.kernel.org" Is there any way to find out why a ceph-osd process takes around 10 times more load on rand 4k writes than on 4k reads? Stefan Am 07.11.2012 21:41, schrieb Stefan Priebe: > Hello list, > > whiling benchmarking i was wondering, why the ceph-osd load is so > extreme high while having random 4k write i/o. > > Here an example while benchmarking: > > random 4k write: 16.000 iop/s 180% CPU Load in top from EACH ceph-osd > process > > random 4k read: 16.000 iop/s 19% CPU Load in top from EACH ceph-osd process > > seq 4M write: 800MB/s 14% CPU Load in top from EACH ceph-osd process > > seq 4M read: 1600MB/s 9% CPU Load in top from EACH ceph-osd process > > I can't understand why in this single case the load is so EXTREMELY high. > > Greets > Stefan