Tuesday, November 13, 2012

IO wait load tracking to a process.

How to identify what processes are generating IO wait load.

An easy way to identify what process is generating your IO Wait load is to enable block I/O debugging. This is done by setting /proc/sys/vm/block_dump to a non zero value like:

echo 1 > /proc/sys/vm/block_dump
This will cause messages like the following to start appearing in dmesg:

bash(6856): dirtied inode 19446664 (ld-2.5.so) on md1
Using the following one-liner will produce a summary output of the dmesg entries:

dmesg | egrep "READ|WRITE|dirtied" | egrep -o '([a-zA-Z]*)' | sort | uniq -c | sort -rn | head
    354 md
    324 export
    288 kjournald
     53 irqbalance
     45 pdflush
     14 portmap
     14 bash
     10 egrep
     10 crond
      8 ncftpput
Once you are finished you should disable block I/O debugging by setting /proc/sys/vm/block_dump to a zero value like:

echo 0 > /proc/sys/vm/block_dump


1) http://www.scriptbits.net/2009/07/how-to-identify-what-processes-are-generating-io-wait-load/

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