Subject: Re: idle RAID1 cpu usage
References: <20061227180900.GA10373@msgid.wurtel.net> <Pine.LNX.4.61.0612271915400.10556@yvahk01.tjqt.qr>
From: Paul Slootman <paul+nospam@wurtel.net>
Organization: Wurtelization
Date: 27 Dec 2006 19:44:09 GMT
Message-ID: <4592cd09$0$339$e4fe514c@news.xs4all.nl>
In-Reply-To: <Pine.LNX.4.61.0612271915400.10556@yvahk01.tjqt.qr>
To: linux-kernel@vger.kernel.org
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1428
Lines: 28

Jan Engelhardt  <jengelh@linux01.gwdg.de> wrote:
>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?).

No, I had rebooted after the initial synchronization was complete.

>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.

On those devices that are actually in use, I'd understand CPU being
used; but where the device is not even mounted or used for swap or
whatever, I find that amount of CPU usage very high for just checking
the bitmap... I may take the idle device apart and reassemble without a
bitmap to see whether that makes any difference.


Paul Slootman
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