Bug 88085 - top reports 0% iowait even when disk heavily used
top reports 0% iowait even when disk heavily used
Product: Red Hat Linux
Classification: Retired
Component: procps (Show other bugs)
i386 Linux
medium Severity medium
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Assigned To: Alexander Larsson
Brian Brock
Depends On:
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Reported: 2003-04-05 07:02 EST by Michael Young
Modified: 2007-04-18 12:52 EDT (History)
3 users (show)

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Fixed In Version:
Doc Type: Bug Fix
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Last Closed: 2003-08-05 05:13:22 EDT
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RHEL 7.3 requirements from Atomic Host:
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Description Michael Young 2003-04-05 07:02:37 EST
From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2.1) Gecko/20030225

Description of problem:
The iowait field in top seems to be stuck at 0.0% even when the machine is under
heavy hard disk load. It looks like what should be reported as iowait is instead
included in the idle figure.
Comment 1 Alexander Larsson 2003-04-07 06:11:44 EDT
Looking at the code it seems top reads the iowait data from the fifth numeric
filed in the /proc/stat cpu line.

However, that field doesn't seem to exist. What's up with this?
Comment 2 Alexander Larsson 2003-04-07 06:15:50 EDT
Ah, this is apparently a 2.5.x kernel extension....
Comment 3 Rik van Riel 2003-07-14 08:45:48 EDT
indeed, iowait statistics is something in the 2.5 kernel (and RHEL)

it is not present in the standard 2.4 kernel
Comment 4 Alexander Larsson 2003-08-05 05:13:22 EDT
So, this will be fixed when we move to 2.6.
Comment 5 Michael Young 2003-08-05 06:03:57 EDT
Yes, indeed it does work if you boot with arjan's test 2.6 kernels.

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