Re: idle array consuming cpu ??!!

[Bill Davidsen <davidsen@tmr.com>]

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.

-- 
Bill Davidsen <davidsen@tmr.com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark