Re: Why is deleting (or reading) files not counted as IO-Wait in top?
- From: David Chinner <dgc@xxxxxxx>
- Date: Mon, 14 Jan 2008 17:24:32 +1100
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
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- From: Matthias Schniedermeyer
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