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Message-ID: <20080114062432.GN155259@sgi.com> Date: Mon, 14 Jan 2008 17:24:32 +1100 From: David Chinner <dgc@....com> To: Matthias Schniedermeyer <ms@...d.de> Cc: linux-kernel@...r.kernel.org Subject: Re: Why is deleting (or reading) files not counted as IO-Wait in top? On Wed, Jan 02, 2008 at 08:35:03PM +0100, Matthias Schniedermeyer 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. Simply because the only I/O that XFS does during a delete is to the log and the log does async I/O and hence the process never blocks in I/O. Instead, it blocks in a far more complex space reservation that may or may not be related to I/O wait.... > So, as 'rm -rf' is essentially a IO (or seek, to be more correct)-bound > task, shouldn't that count as "Waiting for IO"? rm -rf is not seek bound on XFS - it's generally determined by the sequential write speed of the block device or how fast your CPU is.... > The man-page of top says: > 'Amount of time the CPU has been waiting for I/O to complete.' Async I/O means that typically your CPU does not get held up waiting for I/O to complete.... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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