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

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Date:	Thu, 16 Jul 2009 15:12:37 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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

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.

>
> Other than that it does seem to hold up, I've got the patches running on
> my laptop. Don't worry they're not getting lost.

Great.

-- 
Lei Ming
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