Re: High load average on disk I/O on 2.6.17-rc3

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Jason Schoonover wrote:
Hi Robert,

There are, this is the relevant output of the process list:

 ...
 4659 pts/6    Ss     0:00 -bash
 4671 pts/5    R+     0:12 cp -a test-dir/ new-test
 4676 ?        D      0:00 [pdflush]
 4679 ?        D      0:00 [pdflush]
 4687 pts/4    D+     0:01 hdparm -t /dev/sda
 4688 ?        D      0:00 [pdflush]
 4690 ?        D      0:00 [pdflush]
 4692 ?        D      0:00 [pdflush]
 ...

This was when I was copying a directory and then doing a performance test with hdparm in a separate shell. The hdparm process was in [D+] state and basically waited until the cp was finished. During the whole thing there were up to 5 pdflush processes in [D] state.

The 5 minute load average hit 8.90 during this test.

Does that help?

Well, it obviously explains why the load average is high, those D state processes all count in the load average. It may be sort of a cosmetic issue, since they're not actually using any CPU, but it's still a bit unusual. For one thing, not sure why there are that many of them?

You could try enabling the SysRq triggers (if they're not already in your kernel/distro) and doing Alt-SysRq-T which will dump the kernel stack of all processes, that should show where exactly in the kernel those pdflush processes are blocked..

--
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from [email protected]
Home Page: http://www.roberthancock.com/

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