Hi,
Les Mikesell wrote on 2009-07-07 13:45:11 -0500 [Re: [BackupPC-users] Hardware
considerations for building dedicated backuppc server]:
>
> It doesn't make sense to me to consider a process runnable when it is
> waiting for a hardware operation to complete -
I never said a process in state "D" is in state "R". I was talking about the
"load average", as were you in the thread before.
> the scheduler should be ignoring it.
It is.
> I suppose if the disk in question is an IDE that the CPU
> has to micro-manage it might make sense to blame the application for the
> CPU use even if the kernel is doing it.
Are you talking about PIO? You really should get your system to use UDMA. ;-)
No, my point was, the "load average" is an attempt to fit the state of a
system into one single number (which, as we've agreed, is only good for
getting a quick impression, nothing more). I'm sure I don't have to tell
you that a lot of disk activity will make a system more unresponsive than
a lot of processes competing for the CPU. So why just ignore that fact in
the single number?
We don't have to look far for a practical example. The original poster had a
load average of 12 on his system, which fit in with his observation that his
machine was heavily loaded, as you might say. The single number indicated that
something was probably not as it should be. Without taking "D" processes into
account, the load average might have been, say, 0.5. Would that have done the
real situation more justice? Wasn't it exactly the load average, computed the
way it is, that pointed at where to look for the problem?
In what state are processes that are waiting for a page fault to complete?
They're obviously active (as in "wanting to run"), but not runnable. You'd
argue that a faster CPU wouldn't help, because they can't run anyway. I'd
argue that they're part of what is going on (or trying to) on the system.
Let's just disagree on that, ok?
> Yes, the load average in mostly just useful to tell you if a faster CPU
> would help, but it isn't even good for that if it counts things that
> couldn't use the CPU anyway.
I never looked at the load average that way. Where I need to make that
decision, it wouldn't work that way in either case, but I can see that it
could for some people. I'm not sure that was the original intention of
whoever thought up the load average, though.
Regards,
Holger
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