linux-kernel - Re: Problem: Load average of 6, no I/O, 25% idle time. Why?

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Message-Id: <1216459096.7257.2.camel@twins>
Date:	Sat, 19 Jul 2008 11:18:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Timothy Normand Miller <theosib@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Problem: Load average of 6, no I/O, 25% idle time. Why?

On Fri, 2008-07-18 at 18:12 -0400, Timothy Normand Miller wrote:
> On Fri, Jul 18, 2008 at 9:28 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Fri, 2008-07-18 at 08:49 -0400, Timothy Normand Miller wrote:
> >> I have a four processor box, running three compute loads.  The kernel
> >> I'm running is 2.6.25-gentoo-r5.
> >>
> >> One process has four threads, and it's niced to 19.
> >> Another process has one thread and is niced to -10
> >> The last process has one thread and is niced to 0
> >>
> >> One processor is always idle.
> >>
> >> If I change either the 0 to a -10 or the -10 to a zero, then all four
> >> cores are properly utilized.
> 
> Interesting corollary:  If the only thing running is the one nice=19,
> four-thread process, then there's about 4% idle time.  I have to raise
> the priority to get the idle time to go away.  Since when do active
> processes yield to idle time?

They shouldn't... I'm suspecting it might be due to some form of
priority inversion or some such thing.

> Two of my three loads are finished, so when this last one is done,
> I'll try 2.6.26.  Was something like this actively discussed and fixed
> between 2.6.25 and 2.6.26?

Not much, but it has seen drastic change post .26. So if you could also
try Linus' latest -git that would be good.


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