linux-kernel - Re: [PATCH 4/4] perf, x86: Fix event scheduler to solve complex scheduling problems

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Date:	Sun, 17 Apr 2011 10:18:27 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Robert Richter <robert.richter@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] perf, x86: Fix event scheduler to solve complex
 scheduling problems


* Robert Richter <robert.richter@....com> wrote:

> > I'd really prefer not to do this for .39, and I'll have to sit down and 
> > actually read this code. It looks like we went from O(n^2) to O(n!) or 
> > somesuch, also not much of an improvement. I'll have to analyze the solver 
> > to see what it does for 'simple' constraints set to see if it will indeed 
> > be more expensive than the O(n^2) solver we had.
> 
> It wont be more expensive, if there is a solution. But if there is no one we 
> walk all possible ways now which is something like O(n!).

So with 6 counters it would be a loop of 720, with 8 counters a loop of 40320, 
with 10 counters a loop of 3628800 ... O(n!) is not fun.

Thanks,

	Ingo
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