On Wednesday, 2 January 2008 21:35:03 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.
>
> 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
>
The IOWAIT time is the IDLE time that was spent waiting
for I/O. (meaning that there were no tasks running, but some were waiting on
I/O)
Thus if you have another task that is not I/O bound, it can run in that time,
and ideally, you shouldn't notice any I/O slowdown, but the iowait time will
decrease.
It wasn't the case before CFS introduction. I did few tests that showed almost
50% slowdown
when running another task in that iowait time.
It is not longer a problem with CFS.
Regards,
Maxim Levitsky
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