From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: idle array consuming cpu ??!! Date: Wed, 23 Jan 2008 21:16:19 -0500 Message-ID: <4797F4F3.7000903@tmr.com> References: <18323.53904.556620.19761@fisica.ufpr.br> <18323.61999.693738.678224@notabene.brown> <18325.21501.507878.267465@fisica.ufpr.br> <479673E9.8030301@tmr.com> <18326.32105.833682.419778@fisica.ufpr.br> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <18326.32105.833682.419778@fisica.ufpr.br> Sender: linux-raid-owner@vger.kernel.org To: Carlos Carvalho Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Carlos Carvalho wrote: > Bill Davidsen (davidsen@tmr.com) wrote on 22 January 2008 17:53: > >Carlos Carvalho wrote: > >> Neil Brown (neilb@suse.de) wrote on 21 January 2008 12:15: > >> >On Sunday January 20, carlos@fisica.ufpr.br wrote: > >> >> A raid6 array with a spare and bitmap is idle: not mounted and with no > >> >> IO to it or any of its disks (obviously), as shown by iostat. However > >> >> it's consuming cpu: since reboot it used about 11min in 24h, which is quite > >> >> a lot even for a busy array (the cpus are fast). The array was cleanly > >> >> shutdown so there's been no reconstruction/check or anything else. > >> >> > >> >> How can this be? Kernel is 2.6.22.16 with the two patches for the > >> >> deadlock ("[PATCH 004 of 4] md: Fix an occasional deadlock in raid5 - > >> >> FIX") and the previous one. > >> > > >> >Maybe the bitmap code is waking up regularly to do nothing. > >> > > >> >Would you be happy to experiment? Remove the bitmap with > >> > mdadm --grow /dev/mdX --bitmap=none > >> > > >> >and see how that affects cpu usage? > >> > >> Confirmed, removing the bitmap stopped cpu consumption. > > > >Looks like quite a bit of CPU going into idle arrays here, too. > > I don't mind the cpu time (in the machines where we use it here), what > worries me is that it shouldn't happen when the disks are completely > idle. Looks like there's a bug somewhere. That's my feeling, I have one array with an internal bitmap and one with no bitmap, and the internal bitmap uses CPU even when the machine is idle. I have *not* tried an external bitmap. -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark