Date: Sat, 5 Jan 2008 01:31:15 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Matthias Schniedermeyer <ms@citd.de>
Cc: linux-kernel@vger.kernel.org, David Chinner <dgc@sgi.com>,
       Timothy Shimmin <tes@sgi.com>
Subject: Re: Why is deleting (or reading) files not counted as IO-Wait in
 top?
Message-Id: <20080105013115.217a5ab1.akpm@linux-foundation.org>
In-Reply-To: <20080102193503.GA31414@citd.de>
References: <20080102193503.GA31414@citd.de>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1272
Lines: 31

On Wed, 2 Jan 2008 20:35:03 +0100 Matthias Schniedermeyer <ms@citd.de> wrote:

> Hi
> 
> 
> Currently i'm deleting about 500.000 files on a XFS-filesystem which 
> takes a few minutes, as i had a top open i saw that 'wa' is shown as 
> 0.0% (Nothing else running currently) and everything except 'id' is near 
> the bottom too. Kernel is 2.6.23.11.
> 
> So, as 'rm -rf' is essentially a IO (or seek, to be more correct)-bound 
> task, shouldn't that count as "Waiting for IO"?
> 
> The man-page of top says:
> 'Amount of time the CPU has been waiting for I/O to complete.'
> 
> But AFAICT wa only seams to be (ac)counted for writing and not for 
> reading. I come to that conclusion because, when i fire 'sync' i can see 
> some percent wa for a few seconds.
> 

Yes, you would absolutely expect `rm' to be stuck in D state and
contributing to both load average and io-wait in this situation.

I'd think that either XFS is playing games (and it'd take some pretty
inventive games to do this) or your observations are in error.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/