Subject: Re: newidle balancing in NUMA domain?
From: Peter Zijlstra <peterz@infradead.org>
To: Nick Piggin <npiggin@suse.de>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@elte.hu>
In-Reply-To: <20091123114339.GB2287@wotan.suse.de>
References: <20091123112228.GA2287@wotan.suse.de>
	 <1258976175.4531.299.camel@laptop>  <20091123114339.GB2287@wotan.suse.de>
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Date: Mon, 23 Nov 2009 12:50:45 +0100
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On Mon, 2009-11-23 at 12:43 +0100, Nick Piggin wrote:
> On Mon, Nov 23, 2009 at 12:36:15PM +0100, Peter Zijlstra wrote:

> > IIRC this was kbuild and other spreading workloads that want this.
> > 
> > the newidle_idx=0 thing is because I frequently saw it make funny
> > balance decisions based on old load numbers, like f_b_g() selecting a
> > group that didn't even have tasks in anymore.
> 
> Well it is just a damping factor on runqueue flucturations. If the
> group recently had load then the point of the idx is to account
> for this. On the other hand, if we have other groups that are also
> above the idx damped average, it would make sense to use them
> instead. (ie. cull source groups with no pullable tasks).

Right, thing is, I'm still catching up from being gone, and haven't
actually read and tought through the whole rate-limiting thing :-(

If you see a better way to accomplish things, please holler.

> > We went without newidle for a while, but then people started complaining
> > about that kbuild time, and there is a x264 encoder thing that looses
> > tons of throughput.
> 
> So... these were due to what? Other changes in domains balancing?
> Changes in CFS? Something else? Or were they comparisons versus
> other operating systems?

Comparison to Con's latest single-rq spread like there's no cache
affinity BFS thing.


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