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

[Robert Hancock <hancockr@shaw.ca>]

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 hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/

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