linux-kernel - Re: combinatorial explosion in lockdep

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Date:	Wed, 30 Jul 2008 09:21:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Miller <davem@...emloft.net>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: combinatorial explosion in lockdep

On Tue, 2008-07-29 at 23:56 -0700, David Miller wrote:
> From: David Miller <davem@...emloft.net>
> Date: Tue, 29 Jul 2008 21:45:03 -0700 (PDT)
> 
> > If we can agree on this as a fix, it should definitely be backported
> > and submitted for -stable :-)
> > 
> > ----------------------------------------
> > 
> > lockdep: Fix combinatorial explosion in lock subgraph traversal.
> 
> So the next problem I run into is that 8192 is not a large
> enough MAX_LOCKDEP_ENTRIES for this larger cpu count boxes.
> 8192 isn't even big enough for my 64 cpu box.
> 
> It needs to be scaled by NR_CPUS, or something like that.

Or something like that indeed - if distro kernels are going to be build
using NR_CPUS=4096, then these tables might explode - then again,
lockdep is only enabled on -debug kernels anyway...

So yeah.

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