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.