Carlos Carvalho wrote:
Bill Davidsen (davidsen@xxxxxxx) wrote on 22 January 2008 17:53:
>Carlos Carvalho wrote:
>> Neil Brown (neilb@xxxxxxx) wrote on 21 January 2008 12:15:
>> >On Sunday January 20, carlos@xxxxxxxxxxxxxx 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 <davidsen@xxxxxxx>
"Woe unto the statesman who makes war without a reason that will still
be valid when the war is over..." Otto von Bismark
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