Bug 192161 - heavy iowait state
heavy iowait state
Product: Red Hat Enterprise Linux 3
Classification: Red Hat
Component: kernel (Show other bugs)
x86_64 Linux
medium Severity high
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Assigned To: Red Hat Kernel Manager
Brian Brock
: 192162 (view as bug list)
Depends On:
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Reported: 2006-05-17 19:59 EDT by Richard
Modified: 2007-11-30 17:07 EST (History)
2 users (show)

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Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2007-09-13 08:39:55 EDT
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RHEL 7.3 requirements from Atomic Host:
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Description Richard 2006-05-17 19:59:56 EDT
Description of problem:

We have a SUN/v20z(AMD64/x86). When heavy load IO activities done on local or
nfs disks (almost huge file copy), the kernel shows an abnormal IO's activity
with a state which reaches 100% and freezes totally all current processes. 

Version-Release number of selected component (if applicable):

RHEL3/WS - Linux katy 2.4.21-20.ELsmp #1 SMP Wed Aug 18 20:34:58 EDT 2004 x86_64
x86_64 x86_64 GNU/Linux

How reproducible:

Steps to Reproduce:
1. 2 processes performing in parallel a "dd" read/write more than 1GB data with
bs=512 or bs=2M. test this on local disk and nfs disk.
2. while performing, check kernel activity by running a loop of 2s sleep and
check if the 2s sleep does really 2s or more!
2. after each dd i make a 'sync'
3. check out the iowait state, in average it reaches 98/99% and sometimes 100%
and freezes all current processes 
Actual results:
during the heavy io test with dd, the 2s sleep loop does sometimes more than 2s
sleep, it reaches 3s or 5s !! 

Expected results:
a 2s sleep should show 2s sleep even if the kernel is heavily loaded. our server
is running a semi-realtime system and we can't tolerate offset delay >100ms on a
sleep for instance...

Additional info:
Comment 1 Ernie Petrides 2006-05-18 16:21:21 EDT
RHEL3 is now closed.
Comment 2 Ernie Petrides 2006-05-18 16:24:04 EDT
*** Bug 192162 has been marked as a duplicate of this bug. ***
Comment 3 George 2006-07-26 15:25:24 EDT
Same story on RHEL4 update 3 with kernel 2.6.9-34.0.1.EL
Comment 4 Prarit Bhargava 2007-09-13 08:39:55 EDT
Closing re: Comment #1.


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