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

On Mon, May 08, 2006 at 04:55:48PM +0200, Arjan van de Ven wrote:
On Mon, 2006-05-08 at 07:24 -0700, Martin J. Bligh wrote:
It's pretty harmless though. The "load average" thing just means that the
extra pdflush threads are twiddling thumbs waiting on some disk I/O -
they'll later exit and clean themselves up. They won't be consuming
significant resources.

If they're waiting on disk I/O, they shouldn't be runnable, and thus
should not be counted as part of the load average, surely?

yes they are, since at least a decade. "load average" != "cpu
utilisation" by any means. It's "tasks waiting for a hardware resource
to become available". CPU is one such resource (runnable) but disk is
another. There are more ...

... except that any kernel < 2.6 didn't account tasks waiting for disk
IO. Load average has always been somewhat related to tasks contending
for CPU power. It's easy to say "shrug, it changed, live with it", but
at least give applications that want to be nice to the system a way to
figure out the real cpu load.


Erik

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+-- Erik Mouw -- www.harddisk-recovery.com -- +31 70 370 12 90 --
| Lab address: Delftechpark 26, 2628 XH, Delft, The Netherlands
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