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 16:45:15 +0100 Message-ID: <509BD38B.8090200@profihost.ag> References: <509AC772.5010606@profihost.ag> <509BC878.3090804@profihost.ag> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail.profihost.ag ([85.158.179.208]:56137 "EHLO mail.profihost.ag" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751464Ab2KHPpY (ORCPT ); Thu, 8 Nov 2012 10:45:24 -0500 In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Sage Weil Cc: "ceph-devel@vger.kernel.org" Am 08.11.2012 16:01, schrieb Sage Weil: > On Thu, 8 Nov 2012, Stefan Priebe - Profihost AG wrote: >> 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? > > Something like perf or oprofile is probably your best bet. perf can be > tedious to deploy, depending on where your kernel is coming from. > oprofile seems to be deprecated, although I've had good results with it in > the past. I've recorded 10s with perf - it is now a 300MB perf.data file. Sadly i've no idea what todo with it next. > would love to see where the CPU is spending most of it's time. This is > on current master? Yes > I expect there are still some low-hanging fruit that > can bring CPU utilization down (or even boost iops). Would be great to find them. Stefan