linux-kernel - Re: idle RAID1 cpu usage

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Message-ID: <Pine.LNX.4.61.0612271915400.10556@yvahk01.tjqt.qr>
Date:	Wed, 27 Dec 2006 19:18:06 +0100 (MET)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Paul Slootman <paul+nospam@...tel.net>
cc:	linux-kernel@...r.kernel.org
Subject: Re: idle RAID1 cpu usage


On Dec 27 2006 19:09, Paul Slootman wrote:
>
>This works fine, but I noticed that quite some time was being used by
>the mdX_raid1 threads; even on a partition that's not even being used at
>this time... (it was an empty mounted filesystem, but I umounted it to
>be sure the filesystem code wasn't causing some IO).
>
>My question is: why is CPU being used by the RAID1 threads, even for
>those devices that are otherwise unused? What are they doing?

First-time synchronization (if applies), otherwise I suspect some
housekeeping (bitmap perhaps?).
Otherwise it seems like a question who does what. On a raid5 array (i.e.
cpu-heavy), both smbd and mdx_raid5 accumulate time for, of course, xor
calculation.

>I even started distributed-net to check that it wasn't just idle CPU
>cycles that were being used :-)
>
>Note: it did seem that the activity was a bit more during the first
>day after booting; in fact, the mdX_raid1 threads together had used
>about one hour's worth of CPU in the first 24 hours, i.e. 4% CPU
>(according to ps and top).


	-`J'
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