Red Hat Bugzilla – Bug 192161
heavy iowait state
Last modified: 2007-11-30 17:07:10 EST
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
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
during the heavy io test with dd, the 2s sleep loop does sometimes more than 2s
sleep, it reaches 3s or 5s !!
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...
RHEL3 is now closed.
*** Bug 192162 has been marked as a duplicate of this bug. ***
Same story on RHEL4 update 3 with kernel 2.6.9-34.0.1.EL
Closing re: Comment #1.