linux-kernel - Why is deleting (or reading) files not counted as IO-Wait in top?

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Message-ID: <20080102193503.GA31414@citd.de>
Date:	Wed, 2 Jan 2008 20:35:03 +0100
From:	Matthias Schniedermeyer <ms@...d.de>
To:	linux-kernel@...r.kernel.org
Subject: Why is deleting (or reading) files not counted as IO-Wait in top?

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.

Bis denn

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