linux-kernel - Re: [RESEND PATCH 0/11] kernel:lockdep:replace DFS with BFS

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Date:	Thu, 16 Jul 2009 11:54:22 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [RESEND PATCH 0/11] kernel:lockdep:replace DFS with BFS

On Thu, 2009-07-16 at 15:12 +0800, Ming Lei wrote:
> 2009/7/16 Peter Zijlstra <a.p.zijlstra@...llo.nl>:
> >
> > I've asked several times to comment on the removal of that generation
> > count DaveM did. Is that a normal part of DFS, or was that an
> > optimization on top particular to this problem, can something similar be
> > done for BFS, etc.
> 
> DFS uses generation count DaveM did to decide if a class is visted, and BFS
> uses bitmap to mark a class is visted or not and the extra efficiency loss is
> 
>           bitmap_zero(bfs_accessed, MAX_LOCKDEP_ENTRIES);
> 
> before staring each BFS.
> 
> On most of ARCH, bimap_zero can be optimizied to only consume very few
> instructions,
> can't it?
> 
> It seems bitmap is more easily used in BFS than generation count.

Ah, I so missed that, sorry about that.

I'll go over the patches one more time and push them out.

Thanks!

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