linux-kernel - Re: High CPU load when machine is idle (related to PROBLEM: Unusually high load average when idle in 2.6.35, 2.6.35.1 and later)

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Message-ID: <1287582208.3488.20.camel@twins>
Date:	Wed, 20 Oct 2010 15:43:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Damien Wyart <damien.wyart@...e.fr>
Cc:	Chase Douglas <chase.douglas@...onical.com>,
	Ingo Molnar <mingo@...e.hu>, tmhikaru@...il.com,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	Venkatesh Pallipadi <venki@...gle.com>
Subject: Re: High CPU load when machine is idle (related to PROBLEM:
 Unusually high load average when idle in 2.6.35, 2.6.35.1 and later)

On Wed, 2010-10-20 at 15:30 +0200, Peter Zijlstra wrote:
> On Wed, 2010-10-20 at 15:27 +0200, Damien Wyart wrote:
> > 
> > Should'nt we enlarge the list of CC, because for now, responsivity has
> > been close to 0 and it seems we will get a 2.6.36 with buggy load avg
> > calculation. Even if it is only statistics, many supervision tools rely
> > on the load avg, so for production environments, this is not a good
> > thing. 
> 
> It already contains all the folks who know the code I'm afraid.. :/
> 
> I've been playing with it a bit more today, but haven't actually managed
> to make it better, just differently worse..

Ah, I just remembered Venki recently poked at this code too, maybe he's
got a bright idea..

Venki, there are cpu-load issues, the reported issue is that idle load
is too high, and I think I can see that happening with the current code
(due to 74f5187ac8).

The flaw I can see in that commit is that we can go idle multiple times
during the LOAD_FREQ window, which will basically inflate the idle
contribution.

All attempts from me to fix that so far have resulted in curious
results..

Would you have a moment to also look at this?
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