[WBEL-users] iowaits

[Bill Davidsen]

John Hinton wrote:
> I'm still running the 2,4,21-4 kernel on one of my boxes. It has a 
> pretty good load on it. It is dual processor and I notice the iowait is 
> running pretty high. I'm wondering if the stock kernel upgrade has 
> helped regarding this issue?

No, 2.6 will sometimes help a little. The issue is that you now can see 
the waitio instead of having it folded into idle as earlier 2.4 kernels 
did. So you don't really have more, you just see it better.

If your disk i/o and net i/o are reasonable, and you're not swapping you 
butt off, the culprit is moving data in and out of o/s buffers, moving 
to high i/o, etc. If you control the application you can look at what's 
needed to use O_DIRECT on file i/o, on my app it brought the high load 
values down from 25-35% to 8-9%, and I hope to try using sendfile() to 
get rid of some more.

-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me